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## August 23, 2011

### The Set-Theoretic Multiverse

#### Posted by David Corfield

There’s an interesting paper out today on the ArXiv – Joel Hamkins’ The set-theoretic multiverse.

The multiverse view in set theory, introduced and argued for in this article, is the view that there are many distinct concepts of set, each instantiated in a corresponding set-theoretic universe. The universe view, in contrast, asserts that there is an absolute background set concept, with a corresponding absolute set-theoretic universe in which every set-theoretic question has a definite answer. The multiverse position, I argue, explains our experience with the enormous diversity of set-theoretic possibilities, a phenomenon that challenges the universe view. In particular, I argue that the continuum hypothesis is settled on the multiverse view by our extensive knowledge about how it behaves in the multiverse, and as a result it can no longer be settled in the manner formerly hoped for.

So set theorists’ experience of dealing with various models of set theory, and the small modifications needed to generate models either satisfying or not satisfying the continuum hypothesis, tells them that settling its truth or falsity by devising an evident axiom from which either it or its negation follows is not a live option. Gödel’s platonism was wrong then, yet Hamkins retains a form of realism:

The multiverse view is one of higher-order realism – Platonism about universes – and I defend it as a realist position asserting actual existence of the alternative set theoretic universes into which our mathematical tools have allowed us to glimpse. The multiverse view, therefore, does not reduce via proof to a brand of formalism. In particular, we may prefer some of the universes in the multiverse to others, and there is no obligation to consider them all as somehow equal.

Naturally, I looked to see the part Hamkins sees category theory playing in this multiverse. While not extensively considered in the paper, he writes

Set theory appears to have discovered an entire cosmos of set-theoretic universes, revealing a category-theoretic nature for the subject, in which the universes are connected by the forcing relation or by large cardinal embeddings in complex commutative diagrams, like constellations filling a dark night sky. (p. 3)

and

In what appears to be an interesting case of convergent evolution in the foundations of mathematics, this latter universe concept coincides almost completely with the concept of Grothendieck universe, now pervasively used in category theory [Krö01]. The only difference is that the category theorists also view ${V}_{\omega }$ as a Grothendieck universe, which amounts to considering ${\aleph }_{0}$ as an incipient inaccessible cardinal. Surely the rise of Grothedieck universes in category theory shares strong affinities with the multiverse view in set theory, although most set theorists find Grothendieck universes clumsy in comparison with the more flexible concept of a (transitive) model of set theory; nevertheless, the category theorists will point to the multiverse concepts present in the theory of toposes as more general still (see [Bla84]). (p. 13)

Bla84 is Andreas Blass, The interaction between category theory and set theory.

Posted at August 23, 2011 3:18 PM UTC

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### Re: The Set-Theoretic Multiverse

Is “multiverse” really a good term to use? Surely this will unnecessarily attract more physics/quantum mechanics crackpots than you want…

Posted by: asdf on August 23, 2011 5:44 PM | Permalink | Reply to this

### Re: The Set-Theoretic Multiverse

You’ll have to take that up with Joel Hamkins. But your asking caused me to see that William James coined the term multiverse, something I never knew.

Posted by: David Corfield on August 23, 2011 8:12 PM | Permalink | Reply to this

### Re: The Set-Theoretic Multiverse

who works on the subject for decades is a bit strange

Posted by: N Mnev on August 23, 2011 7:42 PM | Permalink | Reply to this

### Re: The Set-Theoretic Multiverse

The page you mention doesn’t mention the word ‘multiverse’, so I don’t see your point. Do you mean the business about

Only set theory allows one to conceive a ‘pure doctrine of the multiple’

in this section?

I can’t say the following is too promising

Badiou’s use of set theory in this manner is not just illustrative or heuristic. Badiou uses the axioms of Zermelo–Fraenkel set theory to identify the relationship of being to history, Nature, the State, and God.

Posted by: David Corfield on August 23, 2011 8:25 PM | Permalink | Reply to this

### Re: The Set-Theoretic Multiverse

I’ve struggled with reading one of Badious texts, I forget which. But I do recall that he talks about turning philosophy away from poetry/romanticism, and embracing mathematics again. He can write well. But the main text I found difficult and turgid.

Although he does focus on the zermelo-fraenkel axioms in the texts I’ve seen, I am aware that he’s used Topos Theory in others.

The philosophers in the seminar I went to were interested in my critique, given that I have some background in mathematics, and they mainly didn’t, of the foundational status of the zermelo-fraenkel axioms.

Posted by: Mozibur Ullah on August 24, 2011 12:06 AM | Permalink | Reply to this

### Re: The Set-Theoretic Multiverse

Badieu has no pop-word multiverse. He has an ontological concept of World. With a contunuum conjecture forcing and topos machinery.
This mainly in his books “Logics of Worlds” and “Being and Event” He is a philosopher but he learned math good enough.

Posted by: N Mnev on August 24, 2011 5:06 AM | Permalink | Reply to this

### Re: The Set-Theoretic Multiverse

What a great paper! I’m immensely encouraged to see at least some ZF-theorists moving towards a view of this sort; arguably, it is long overdue. (My personal philosophy tends more towards formalism than Platonism, but given that one is a Platonist, the “multiverse” view seems to me much more defensible and useful than the “universe” one.) I’m particularly happy that he extends his pluralism explicitly to “the” natural numbers, and I very much appreciate his argument for the impossibility of “settling” the continuum hypothesis:

Our situation, after all, is not merely that CH is formally independent and we have no additional knowledge about whether it is true or not. Rather, we have an informed, deep understanding of the CH and ¬CH worlds and of how to build them from each other…. Consequently, if you were to present a principle Φ and prove that it implies ¬CH, say, then we can no longer see Φ as obviously true, since to do so would negate our experiences in the set-theoretic worlds having CH. … The situation would be like having a purported ‘obviously true’ principle that implied that midtown Manhattan doesn’t exist. But I know it exists; I live there. Please come visit!

Of course, this argument could just as well be extended to the axiom of choice and the law of excluded middle. ZFC-theorists may not be as familiar with the universes in which these fail, but constructive mathematicians and topos theorists are quite familiar with them.

Along those lines, around here it seems appropriate to emphasize further the point that

category theorists will point to the multiverse concepts present in the theory of toposes as more general still

Since models of ZFC are entirely first-order equivalent to models of ETCS + Replacement, the multiverse of models of ZFC might just as well be considered a multiverse of models of ETCS+R. The latter view, of course, has the advantage that we can consider functors and transformations between models of ETCS+R, making the multiverse into a 2-category.

I’m also intrigued by his brief description of the “modal logic of forcing”, which I don’t recall having encountered before. I wonder whether this modal logic is at all related to some sort of internal logic of a multiverse 2-category.

Posted by: Mike Shulman on August 24, 2011 6:50 AM | Permalink | Reply to this

### Re: The Set-Theoretic Multiverse

[…] making the multiverse into a 2-category.

Which then also provides a good solution to the problem that asdf sees above.

Let’s not say “multiverse”. Let’s say “2-category” of set theory models.

Posted by: Urs Schreiber on August 24, 2011 8:51 AM | Permalink | Reply to this

### Re: The Set-Theoretic Multiverse

As I understand it, forcing conditions can be understood as a kind of Kripke model. Suppose you have a ZFC model $M$, to which you wish to add a new generic element $G$. So, staying in $M$, you construct a poset of approximations (whose elements I will write $g,h$) of the new generic element $G$. Then, propositions $\varphi$ interpreted $M\left[G\right]$ are translated into formulas $g⊩\varphi$, with the usual Kripke monotonicity condition that if $g\le h$ (i.e., $g$ is a more precise approximation than $h$)and $h⊩\varphi$, then $g⊩\varphi$. And of course, if you have a nontrivial Kripke structure you get interesting modalities.

I’ve never used proper Cohen forcing (I only really know it via realizability models of classical logic), so this explanation might be off in some details.

Posted by: Neel Krishnaswami on August 24, 2011 9:21 AM | Permalink | Reply to this

### Re: The Set-Theoretic Multiverse

Yes, forcing with a single set of forcing conditions is very similar to Kripke models. Both are special cases of the construction of sheaves on a site: Kripke models are presheaves on a poset, while forcing is sheaves for the double-negation topology on a poset.

However, from reading the paper, it looks like what Joel means by the “modal logic of forcing” involves rather modalities that quantify over all possible forcing conditions. He writes $♢\varphi$ to mean “$\varphi$ holds in some forcing extension”, and “$\square \varphi$” to mean “$\varphi$ holds in all forcing extensions”. Have a look at section 10.

Posted by: Mike Shulman on August 24, 2011 4:59 PM | Permalink | Reply to this

### Re: The Set-Theoretic Multiverse

The modal logic of forcing explains at greater length. The logic is S4.2, see Theorem 3.

From the quotation in my post, there are also large cardinal embeddings. I wonder if there’s a modality for large cardinal embeddings. Are there any other kinds of arrow between universes?

Why do we not introduce modal concepts in other categories? E.g., in the category of groups one could say a property is necessarily held by a group if it is held at all codomains of arrows whose domain is that group.

Posted by: David Corfield on August 24, 2011 5:38 PM | Permalink | Reply to this

### Re: The Set-Theoretic Multiverse

Are there any other kinds of arrow between universes?

Sure: logical functors come to mind from a topos-theoretic perspective, or the “inclusion” $L\subseteq V$ and its relatives. (I put “inclusion” in quotes, because considered as a functor between models of ETCS, it’s faithful but not full.) Maybe the multiverse is more than just a 2-category? There’s a very natural proarrow equipment consisting of toposes, geometric morphisms, and lex functors, and I think all these other sorts of morphism are probably particular kinds of lex functors; I wonder whether they can be identified from the structure of that proarrow equipment?

E.g., in the category of groups one could say a property is necessarily held by a group if it is held at all codomains of arrows whose domain is that group.

Well, the category of groups has a zero object, so there is a morphism from any group to any other group; thus the only necessary closed sentences would be those that hold of all groups. That’s going to be true of many “algebraic” categories.

One thing to do would be to restrict the morphisms and consider only quotients, or only subgroups, and we do occasionally talk about modalities of this sort. For instance, a property is sometimes called “hereditary” if it is inherited by all subobjects.

Alternatively, we may get interesting things by thinking of properties of elements. For instance, I think an element of a ring is “possibly invertible” just when it lies outside of some maximal ideal. Maybe the modal logic of categories is worthy of further thought? It might be an interesting unifying principle.

Posted by: Mike Shulman on August 24, 2011 11:36 PM | Permalink | Reply to this

### Re: The Set-Theoretic Multiverse

Alternatively, we may get interesting things by thinking of properties of elements.

I was wondering, during the last bout of modal logic thinking, how one might need to augment modal logic in the first order case if there are multiple arrows from one object to another. For an element of an object, you would want to express the difference between some property holding at images: for every arrow from that object; for every arrow to some object; for some arrow to every object; for some arrow to some object.

In the topological semantics approach, this plays on the possibility of multiple counterparts at another fibre of an element of a fibre, according to the path taken in the base space.

Posted by: David Corfield on August 25, 2011 8:59 AM | Permalink | Reply to this

### Re: The Set-Theoretic Multiverse

I don’t really understand. I was thinking that if $\varphi$ is a property saying something about an object $A$ and possibly its elements, then $\square \varphi$ means that (for any object $B$ and) for any morphism $f:A\to B$, the corresponding property to $\varphi$ (pushed forwards along $f$) holds of $B$. And that $♢\varphi$ means that (for some object $B$ and) for some morphism $f:A\to B$, the corresponding property to $\varphi$ (pushed forwards along $f$) holds of $B$. How does that correspond to your English phrasings?

Posted by: Mike Shulman on August 27, 2011 2:37 AM | Permalink | Reply to this

### Re: The Set-Theoretic Multiverse

In first-order modal logic, there is a notion of a collection of worlds related by an accessibility relation, and for each world a set of individuals, satisfying various properties. Then, according to David Lewis’s counterpart theory, counterfactual statements are made true by the state of affairs concerning counterparts in other possible worlds.

So, “Had I taken an aspirin, I wouldn’t have a headache now” is made true by events in the closest possible world to ours in which my counterpart took an aspirin, so long as there he has no headache.

Leaving aside the metaphysics of it all, there could be something useful in devising a model made up of a collection of worlds, related to each other in a certain way, and a collection of individuals at each world, such that I may be able to speak of $x$ in world 1 having a counterpart $y$ in world 2. Then we could wonder whether world 2 might contain more than one counterpart of $x$. (This sort of property is considered in Principles that are not accepted in normal CT.)

Then we might consider a copresheaf of individuals over a category of worlds, and for $x$ at object $A$, two counterparts of $x$ at object $B$, according to different morphisms $f,g:A\to B$. Then the modal properties of $x$ are not restricted to ‘at all worlds all counterparts of $x$…’, and ‘at some world some counterpart of $x$…’. There are also ‘at all worlds some counterpart of $x$…’, and ‘at some world all counterparts of $x$…’.

Posted by: David Corfield on August 30, 2011 10:46 AM | Permalink | Reply to this

### Re: The Set-Theoretic Multiverse

Can you give any non-metaphysical examples of where such modal properties might be useful? It seems more natural to me to quantify over objects and morphisms at the same time (that is, to quantify over objects in a slice category).

Posted by: Mike Shulman on September 1, 2011 5:05 PM | Permalink | Reply to this

### Re: The Set-Theoretic Multiverse

If we’re just talking about objects and morphisms, might I not be interested in a space $X$ and a subspace $Y$, and ask of $X$’s Moore path category whether it is the case that from a given object $x$, for every object there is a morphism to it only meeting $Y$ if at all at its endpoints? And I might wonder if for some object every morphism to it from $x$ avoids $Y$.

Seems like the flexibility our old friend dependent type theory gives us.

Posted by: David Corfield on September 1, 2011 5:39 PM | Permalink | Reply to this

### Re: The Set-Theoretic Multiverse

Okay; I guess I see how you could call that a “modal property”. I don’t think I (yet) gain anything conceptually from thinking about it that way, though. With the ones I was calling $\square$ and $♢$, I can see how the English modal words “necessarily” and “possibly” more or less fit the mathematical meanings.

Posted by: Mike Shulman on September 6, 2011 6:45 PM | Permalink | Reply to this

### Re: The Set-Theoretic Multiverse

…making the multiverse into a 2-category.

So what kind of 2-category is it? A while ago we spoke of models of ETCS as forming the 2-category of well-pointed toposes with a natural numbers object satisfying the axiom of choice. Is replacement expressible naturally in category theoretic terms? Will there be a forgetful functor from models of ETCS + R to models of ETCS, and then a left adjoint?

Can one do a Tannakian trick and extract a theory of sets from its 2-category of models?

Posted by: David Corfield on August 24, 2011 9:54 AM | Permalink | Reply to this

### Re: The Set-Theoretic Multiverse

There are category-theoretic ways to express replacement; one of these days I’ll get around to nLabifying them. The one I like best is in my paper on stack semantics.

Will there be a forgetful functor from models of ETCS + R to models of ETCS, and then a left adjoint?

I would say certainly yes, and probably not, respectively. ETCS+R is proof-theoretically stronger than ETCS, so if I just give you a model of ETCS, then you can’t construct from it any model of ETCS+R—unless either ETCS is inconsistent, or you make use of an ambient theory that’s at least as strong as ETCS+R. (As an example of the latter, in a sufficiently strong ambient theory you could consider a category of (pre)sheaves on your (small) model of ETCS, then do some sort of ultrapower to make yourself well-pointed again, but something like that seems to me unlikely to produce such an adjoint.)

Actually, from this perspective, I think it’s more natural to consider the 2-category of Boolean topoi with NNO and satisfying internal AC—i.e. topoi whose internal logic (or, more precisely, stack semantics) validates ETCS. (The stack-semantics version of replacement is called being “autological”.) When we move “into” a given universe, that means working in its internal logic, from which viewpoint it automatically “looks” well-pointed. But from the “external” viewpoint of the multiverse, there’s no need to demand anything be well-pointed, especially since most interesting constructions on topoi don’t preserve well-pointedness.

However, I think that modification is unlikely to change the situation regarding adjoints.

Can one do a Tannakian trick and extract a theory of sets from its 2-category of models?

My initial reaction is that all of these universes of sets are models of a single theory, so there is no reconstruction to be done. But maybe I misunderstand?

Posted by: Mike Shulman on August 24, 2011 7:03 PM | Permalink | Reply to this

### Re: The Set-Theoretic Multiverse

I meant more the idea of reconstructing a theory from its collection of models, as in extracting the theory of groups from $\mathrm{Grp}$, or in Awodey and Forssell’s logical duality.

If I give you the 2-category (or whatever) of models of ETCS, can you reconstruct ETCS?

Posted by: David Corfield on August 25, 2011 8:48 AM | Permalink | Reply to this

### Re: The Set-Theoretic Multiverse

I meant more the idea of reconstructing a theory from its collection of models

Yes, that’s what I thought you meant. What I meant was, there’s only one theory around (ETCS). But I guess we could consider it inside the class of first-order logical theories, and apply any general result to that. I don’t know exactly what sort of morphism between models of ETCS you would get falling out of that, though; I kind of suspect the resulting “category of models of ETCS” would not be any of the usual ones we like to think about. But I could be wrong.

Posted by: Mike Shulman on August 27, 2011 2:34 AM | Permalink | Reply to this

### Re: The Set-Theoretic Multiverse

I can’t resist quoting one more lovely passage from the article:

In algebra, when one group is constructed from another or when a field is constructed as a quotient of a ring, these new structures are taken to be perfectly good groups and fields. There is no objection in such a case announcing “but that isn’t the real $+$” analogous to what one might hear about a nonstandard or disfavored set-membership relation: “that isn’t the real $\in$.” Such remarks in set theory are especially curious given that the nature and even the existence of the intended absolute background notion is so murky.

Posted by: Mike Shulman on August 25, 2011 4:24 AM | Permalink | Reply to this

### Re: The Set-Theoretic Multiverse

Well, I’ve got a naive question: doesn’t each axiomatic formulation of set theory correspond to a different (albeit “equivalent” in some sense) version of the topos Set?

Posted by: Alex on August 27, 2011 4:35 PM | Permalink | Reply to this

### Re: The Set-Theoretic Multiverse

Any given model of any given (membership-based) set theory produces a category of sets. Different models of the same set theory may produce inequivalent categories, although the categories will share the same basic properties provable from the axioms of that set theory (like being a well-pointed topos, for instance).

Models of different membership-based set theories, on the other hand, may produce categories of sets that differ in their basic properties. For instance, whether or not the axiom of choice is assumed determines whether all epimorphisms in Set are necessarily split.

But on the third hand, models of two different set theories could produce equivalent categories of sets. For instance, the category of sets in a model of a non-well-founded set theory, and its subcategory of well-founded sets (which form a model of a well-founded set theory), will often be equivalent—for if we assume AC, then every set is bijective to a well-founded one (namely, a von Neumann ordinal).

On the fourth hand, for a large swath of membership-based set theories, the model of the original theory (assuming we fix a particular theory) can be recovered from the resulting category of sets, by constructing explicit membership trees; see the nLab entry pure set.

Posted by: Mike Shulman on August 29, 2011 6:02 AM | Permalink | Reply to this

### Re: The Set-Theoretic Multiverse

It’s sometimes useful to have a popularised article as a starting point for further exploration. New Scientist is usually rather bad on math, but they did put Joel Hamkin’s idea nicely into context by quoting him in this article

Posted by: M. on September 5, 2011 7:50 AM | Permalink | Reply to this

### Re: The Set-Theoretic Multiverse

The multiverse view, therefore, does not reduce via proof to a brand of formalism. In particular, we may prefer some of the universes in the multiverse to others, and there is no obligation to consider them all as somehow equal.

The phrasing suggests that formalists cannot prefer some formal systems or models thereof to others and must feel some obligation to consider them all as somehow equal. I don't know any formalists like that.

Posted by: Toby Bartels on December 31, 2011 9:40 AM | Permalink | Reply to this

Post a New Comment


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# Mass distribution of a moving body

Perhaps it is a simple question, but I am unable to solve it. Let us suppose that we have a body confined in $$\textbf{R}^{3}$$ whose mathematical description is given by a bounded and closed domain $$\textbf{D}\subset\textbf{R}^{3}$$. Moreover, let us also suppose that its mass distribution is given by the function $$m:\textbf{D}\rightarrow\textbf{R}_{\geq0}$$ such that \begin{align*} \int_{\textbf{D}}m(x,y,z)\mathrm{d}x\mathrm{d}y\mathrm{d}z = M > 0 \end{align*}

My question is: given that its center of mass' trajectory is described by the curve $$\alpha:[0,1]\rightarrow\textbf{R}^{3}$$, how do we describe the mass distribution $$m(x,y,z,t)$$ along time?

It is worth mentioning here that we are not considering any kind of rotation, and we are dealing with a rigid body.

• You does not provide enough information for this to be solved. Even if it is a rigid body (it does not deforms in any way), you need to know how it rotates. – b.Lorenz Dec 21 '18 at 20:19
• Thank you for the comment. I forgot to mention that I am not considering rotations of any kind. Besides, it is a rigid body. – APC89 Dec 21 '18 at 20:20
• Please edit that into question body – b.Lorenz Dec 21 '18 at 20:21
• I think it's really simple if you can set the origin to the center of mass, then it's just a coordinate shift. – Jasper Dec 21 '18 at 20:32
• @Jasper That should have been an answer, not a comment. – Aaron Stevens Dec 23 '18 at 3:34

$$m_{timedependent}(\mathrm{r},t) = m_{initial}( \mathrm{r} -\alpha(t))$$

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# PSR-Duh!

In a previous lesson here on Nettuts+, you learn about PSR; however, that article didn't detail the process of integrating that coding style into your projects. Let's fix that!

Note: this article assumes that you've read PSR-Huh?, and understand what PSR refers to. Let's begin with the first standard: PSR-0.

The PHPCS plugin is the most helpful tool I've used.

In the past, we included PHP files in one of two ways:

• Using a giant block of include statements at the top of each file.
• List all includes in a single file and include that single file within your project.

There are pros and cons to both of these approaches, but, I think we can all agree that neither are optimal or modern solutions. PHP5 introduced the concept of autoloading files based on their class names; so, PSR-0 aims to keep filenames consistent.

Namespaces have nothing to do with filenames or autoloading; you can technically declare different namespaces in the same file. For example, the following code is perfectly valid.

There are two Hello classes in this single file, but they reside within different namespaces. The final two lines of this code instantiate the Hello() classes on their respective namespaces. The first outputs "Nettuts+", while the second echos "Gabriel." Namespaces allow you to differentiate between two classes with the same name, much like you might be used to with folders on your desktop. The PSR-0 standard simply leverages the benefits of namespaces, making it easy to autoload your classes. By consistently naming your files, you can create a function that locates the necessary files automatically.

To be PSR-1 compliant, you also must follow PSR-0.

Be sure to read the full standard, but to summarize:

• Each class must be namespaced with the project's (or creator's) name.
• Underscores within the class' name should be converted to directory separators.
• Files must have the .php extension.

For example, a class reference of:

if following PSR-0, should translate to this path:

How might we implement this functionality? The most obvious solution is to use Composer, which ships with a PSR-0 compliant autoloader. If you leverage Composer in your projects (and you should), then opt for its autoloader, rather than writing your own.

A PSR-0 compliant loader allows you to specify a base path, informing the loader which directory to look in first. To get started, create a simple composer.json file that contains the following JSON:

This JSON file tells Composer that we want to use the PSR-0 standard to autoload all Nettuts-namespaced files with the current directory (the root folder) as the base path. We also want to autoload all classes with the Gmanricks namespace, relative to the vendor folder (e.g. ./vendor/Gmanricks/ClassName).

Now, type "composer install" to generate the autoload classes, or "composer dump-autoload" on subsequent edits to regenerate the autoload classes. Also, don't forget to require the autoloader somewhere early in your project.

Composer is your best option, but there may be scenarios when you want a small, simple autoloader. The PHP-FIG provides a sample autoloader that you can use:

It's important to note that this loader attempts to load all classes using the PSR standard in the current directory.

Now that we're successfully autoloading classes, let's move on to the next standard: the basic coding standard.

## PSR-1 - The Basic Coding Standard

PSR-1 defines general coding guidelines, which can be divided into two parts.

### Naming Conventions

Namespaces allow you to differentiate between two classes with the same name.

As with any programming language, following naming conventions ultimately makes your code easier to read and maintain. Here's a few rules to follow:

• Class names use PascalCase.
• Method names should be in camelCase.
• Constants require all capital letters, separating each word with an underscore (e.g. CONSTANT_VARIABLE).

### Code Conventions:

There's more to it than naming conventions; follow these guidelines as well:

• Only use <?php or <?= in your code. Don't close PHP within a class.
• Files should either declare symbols or use them.
• Files must be in UTF-8 format without BOM for PHP code

Most of these are self-explanatory, but the middle convention is slightly confusing. It essentially dictates that any declaration, be it functions, classes, etc., should be separated into their own files. This not only promotes best practices like code-reuse and separation, but it keeps your code neat and clean.

It's worth mentioning that each PSR standard builds upon the previous PSR standard. As such, to be PSR-1 compliant, you also must follow PSR-0. By following these two standards, your code will be properly namespaced and autoloaded. There really isn't a reason not to follow them.

Yes, some developers complain about PSR and prefer to follow other conventions, but by following this standard, you can share code with everyone without worrying about its consistency. Having said that, nobody is forcing your hand here. It's simply a recommended guideline.

The next standard, PSR-2, dives into the specifics of how you should structure your code.

## PSR-2 - The Advanced Coding Standard

PSR-2 dives into the specifics of how you should structure your code.

Next, we come to the one standard that PHP developers struggle with most; in fact, it's the reason why I chose to write this article.

PSR-2 defines many rules, many of which are listed below:

• Four spaces should be used instead of tabs.
• The ideal line length should be under 80 characters, but a soft limit of 120 characters should be imposed on all lines.
• There should be one blank line under the namespace and use declarations.
• A method's or class' opening brace must be on its own line.
• A method's or class' closing brace must go on the line immediately after the body.
• All properties and methods require a visibility level.
• The 'abstract' / 'final' keywords should appear before the visibility while 'static' goes after.
• Control structure keywords must be followed by one space.
• A control statement's opening brace should appear on the same line as the statement.

Be sure to view the entire spec for a complete overview.

PSR-2 is just as important as PSR-1 (and PSR-0). It intends to make code easy to read and maintain. But, as they say, "The devil is in the details." There are a lot of details to remember, which can be difficult if your programming habits differ from what the standard defines. Thankfully, if you're on board, there are tools that help you adhere to PSR-0, PSR-1 and PSR-2. Perhaps the best tool is the Sublime Text plugin, PHPCS.

## PHPCS - PHP Code Sniffer

The PHPCS plugin is the most helpful tool I've used, when it comes to getting code into shape. It allows you to not only ensure that your code follows the PSR standards, but it also uses PHP's linter to check for syntax errors. This is a great time saver; you no longer have to worry about syntax errors when you test your code in the browser.

Install the package through Sublime Package Control (it's called Phpcs), or, alternatively, with Git, using the following commands:

This installs the plugin, but you need a few dependencies before you can configure PHPCS. Once again, the easiest way to install them is with Composer. Browse to a directory of your choice and create a composer.json file with the following JSON:

This installs the three dependencies into the current folder. Open a terminal window to your installation location and type composer install, and it will download the necessary packages.

Now you can configure the plugin in Sublime Text. Navigate to 'Preferences' > 'Package Settings' > 'PHP Code Sniffer' > 'Settings - User'.

The plugin needs to know where the three dependencies reside, as well as the standard that we want our code to adhere to:

These settings inform PHPCS that we want to ahere to the PSR2 standard and provide each dependency's path. Don't forget to replace DEPENDENCY_PATH with your actual path.

Restart Sublime, and the code sniffer will scan your code when you save your PHP files.

Right-clicking in the editor will also list several new options, such as clearing error marks and attempting to fix the non-standard issues. However, considering that the point of this article is to get you used to the standard, I suggest manually fixing your code and avoiding the automatic fixer feature.

## Conclusion

The PSR standards were created so that code could easily be reused from project to project, without sacrificing on code style consistency. While they may feel overwhelming at first, you can use the ideas and tools from this article to help you make the transition.

To reiterate one last time: nobody is forcing you to change the way that you code in PHP. It's simply a guide, originally meant for framework interoperability. That said, at Nettuts+, we consider it a best practice to follow. Now make up your own mind! If you have any questions, let's hear them below!


text:
# PrepperPatriot.com #Preparedness #Survivalist Wiki-Blog for #MAGA #AmericaFirst Patriots

### Site Tools

tsunami
Snippet from Wikipedia: Tsunami

A tsunami ( (t)soo-NAH-mee, (t)suu-; from Japanese: 津波, lit. 'harbour wave', pronounced [tsɯnami]) is a series of waves in a water body caused by the displacement of a large volume of water, generally in an ocean or a large lake. Earthquakes, volcanic eruptions and other underwater explosions (including detonations, landslides, glacier calvings, meteorite impacts and other disturbances) above or below water all have the potential to generate a tsunami. Unlike normal ocean waves, which are generated by wind, or tides, which are generated by the gravitational pull of the Moon and the Sun, a tsunami is generated by the displacement of water.

Tsunami waves do not resemble normal undersea currents or sea waves because their wavelength is far longer. Rather than appearing as a breaking wave, a tsunami may instead initially resemble a rapidly rising tide. For this reason, it is often referred to as a tidal wave, although this usage is not favoured by the scientific community because it might give the false impression of a causal relationship between tides and tsunamis. Tsunamis generally consist of a series of waves, with periods ranging from minutes to hours, arriving in a so-called "wave train". Wave heights of tens of metres can be generated by large events. Although the impact of tsunamis is limited to coastal areas, their destructive power can be enormous, and they can affect entire ocean basins. The 2004 Indian Ocean tsunami was among the deadliest natural disasters in human history, with at least 230,000 people killed or missing in 14 countries bordering the Indian Ocean.

The Ancient Greek historian Thucydides suggested in his 5th century BC History of the Peloponnesian War that tsunamis were related to submarine earthquakes, but the understanding of tsunamis remained slim until the 20th century and much remains unknown. Major areas of current research include determining why some large earthquakes do not generate tsunamis while other smaller ones do; accurately forecasting the passage of tsunamis across the oceans; and forecasting how tsunami waves interact with shorelines.

, An aerial view of damage in the Sendai region with black smoke coming from the Nippon Oil Sendai oil refinery]]

A tsunami (plural: tsunamis or tsunami; from

, lit. “harbour wave”;<ref>

  {{cite web|url=http://nthmp-history.pmel.noaa.gov/terms.html
|title=Tsunami Terminology
|publisher=[[NOAA]]|accessdate=2010-07-15}}
English pronunciation:

or

<ref>

  {{cite book
|title=Longman pronunciation dictionary
|first=John C. |last= Wells
|publisher=Longman |location=Harlow, England
|year=1990 |isbn=0-582-05383-8 |page=736
}} Entry: "tsunami")
is a series of water waves caused by the displacement of a large volume of a body of water, generally an ocean or a large lake. Earthquakes, volcanic eruptions and other underwater explosions (including detonations of underwater nuclear devices), landslides, glacier calvings, meteorite impacts and other disturbances above or below water all have the potential to generate a tsunami.<ref>

</ref>

Tsunami waves do not resemble normal sea waves, because their wavelength is far longer. Rather than appearing as a breaking wave, a tsunami may instead initially resemble a rapidly rising tide, and for this reason they are often referred to as tidal waves. Tsunamis generally consist of a series of waves with periods ranging from minutes to hours, arriving in a so-called “wave train”.<ref name=“Fradin 2008”>

  {{cite book|last=Fradin|first=Judith Bloom and Dennis Brindell
|title=Witness to Disaster: Tsunamis
|publisher=[[National Geographic Society]]
|location=Washington, D.C.|year=2008
|series=Witness to Disaster|pages=42, 43
|url=http://shop.nationalgeographic.com/ngs/product/books/kids-books-and-atlases/animals-and-nature/witness-to-disaster%3A-tsunamis}}
</ref> Wave heights of tens of metres can be generated by large events. Although the impact of tsunamis is limited to coastal areas, their destructive power can be enormous and they can affect entire ocean basins; the 2004 Indian Ocean tsunami was among the deadliest natural disasters in human history with over 230,000 people killed in 14 countries bordering the Indian Ocean.

The Greek historian Thucydides suggested in his late 5th century BC, History of the Peloponnesian War, that tsunamis were related to submarine earthquakes,<ref name=“Thucydides 3.89.1-4”/><ref name=“Smid, T. C. 103f.”/> but the understanding of a tsunami's nature remained slim until the 20th century and much remains unknown. Major areas of current research include trying to determine why some large earthquakes do not generate tsunamis while other smaller ones do; trying to accurately forecast the passage of tsunamis across the oceans; and also to forecast how tsunami waves would interact with specific shorelines.

## Etymology

in Acehnese and Indonesian]]

The term tsunami comes from the Japanese 津波, composed of the two kanji (tsu) meaning “harbour” and (nami), meaning “wave”. (For the plural, one can either follow ordinary English practice and add an s, or use an invariable plural as in the Japanese.<ref>[a. Jap. tsunami, tunami, f. tsu harbour + nami waves.—Oxford English Dictionary]</ref>)

Tsunami are sometimes referred to as tidal waves, which are unusually high sea waves that are triggered especially by earthquakes.<ref>http://www.merriam-webster.com/dictionary/tidal%20wave</ref> In recent years, this term has fallen out of favor, especially in the scientific community, because tsunami actually have nothing to do with tides. The once-popular term derives from their most common appearance, which is that of an extraordinarily high tidal bore. Tsunami and tides both produce waves of water that move inland, but in the case of tsunami the inland movement of water is much greater and lasts for a longer period, giving the impression of an incredibly high tide. Although the meanings of “tidal” include “resembling”<ref>“Tidal”, The American Heritage Stedman's Medical Dictionary. Houghton Mifflin Company. 11 November 2008.Dictionary.reference.com</ref> or “having the form or character of”<ref>-al. (n.d.). Dictionary.com Unabridged (v 1.1). Retrieved November 11, 2008, Dictionary.reference.com</ref> the tides, and the term tsunami is no more accurate because tsunami are not limited to harbours, use of the term tidal wave is discouraged by geologists and oceanographers.

There are only a few other languages that have an equivalent native word. In Acehnese language, the words are ië beuna<ref>Proposing The Community-Based Tsunami Warning System</ref> or alôn buluëk<ref>Novel Alon Buluek</ref> (depending on the dialect). In Tamil language, it is aazhi peralai. On Simeulue island, off the western coast of Sumatra in Indonesia, in Devayan language the word is smong, while in Sigulai language it is emong.<ref>Tsunami 1907: Early Interpretation and its Development</ref> In Singkil (in Aceh province) and surrounding, the people name tsunami with word gloro.<ref>13 Pulau di Aceh Singkil Hilang</ref>

## History

in 1755]]

in Japan, with their ships tossed inland by a tsunami, meeting some Japanese in 1779]]

As early as 426 BC the Greek historian Thucydides inquired in his book History of the Peloponnesian War about the causes of tsunami, and was the first to argue that ocean earthquakes must be the cause.<ref name=“Thucydides 3.89.1-4”>Thucydides: “A History of the Peloponnesian War”, 3.89.1–4</ref><ref name=“Smid, T. C. 103f.”>

</ref>

“The cause, in my opinion, of this phenomenon must be sought in the earthquake. At the point where its shock has been the most violent the sea is driven back, and suddenly recoiling with redoubled force, causes the inundation. Without an earthquake I do not see how such an accident could happen.”<ref name=“Thucydides 3.89.5”>Thucydides: “A History of the Peloponnesian War”, 3.89.5</ref>

The Roman historian Ammianus Marcellinus (Res Gestae 26.10.15-19) described the typical sequence of a tsunami, including an incipient earthquake, the sudden retreat of the sea and a following gigantic wave, after the 365 AD tsunami devastated Alexandria.<ref name=“Kelly, Gavin (2004)”>

</ref><ref name=“Stanley, Jean-Daniel & Jorstad, Thomas F. (2005)”>Stanley, Jean-Daniel & Jorstad, Thomas F. (2005), “The 365 A.D. Tsunami Destruction of Alexandria, Egypt: Erosion, Deformation of Strata and Introduction of Allochthonous Material”</ref>

While Japan may have the longest recorded history of tsunamis, the sheer destruction caused by the 2004 Indian Ocean earthquake and tsunami event mark it as the most devastating of its kind in modern times, killing around 230,000 people. The Sumatran region is not unused to tsunamis either, with earthquakes of varying magnitudes regularly occurring off the coast of the island.<ref>The 10 most destructive tsunamis in history, Australian Geographic, March 16, 2011.</ref>

==Generation mechanisms==<!– Ocean surface wave links here. –> The principal generation mechanism (or cause) of a tsunami is the displacement of a substantial volume of water or perturbation of the sea.<ref>

</ref> This displacement of water is usually attributed to either earthquakes, landslides, volcanic eruptions, glacier calvings or more rarely by meteorites and nuclear tests.<ref>

</ref><ref>

</ref> The waves formed in this way are then sustained by gravity. Tides do not play any part in the generation of tsunamis.

### Seismicity

Tsunami can be generated when the sea floor abruptly deforms and vertically displaces the overlying water. Tectonic earthquakes are a particular kind of earthquake that are associated with the Earth's crustal deformation; when these earthquakes occur beneath the sea, the water above the deformed area is displaced from its equilibrium position.<ref>

</ref> More specifically, a tsunami can be generated when thrust faults associated with convergent or destructive plate boundaries move abruptly, resulting in water displacement, owing to the vertical component of movement involved. Movement on normal faults will also cause displacement of the seabed, but the size of the largest of such events is normally too small to give rise to a significant tsunami.

<gallery mode=“packed”> File:Eq-gen1.svg|Drawing of tectonic plate boundary before earthquake File:Eq-gen2.svg|Overriding plate bulges under strain, causing tectonic uplift. File:Eq-gen3.svg|Plate slips, causing subsidence and releasing energy into water. File:Eq-gen4.svg|The energy released produces tsunami waves. </gallery>

Tsunamis have a small amplitude (wave height) offshore, and a very long wavelength (often hundreds of kilometres long, whereas normal ocean waves have a wavelength of only 30 or 40 metres),<ref>Facts and figures: how tsunamis form, Australian Geographic, March 18, 2011.</ref> which is why they generally pass unnoticed at sea, forming only a slight swell usually about

above the normal sea surface. They grow in height when they reach shallower water, in a wave shoaling process described below. A tsunami can occur in any tidal state and even at low tide can still inundate coastal areas.

On April 1, 1946, a magnitude-7.8 (Richter Scale) earthquake occurred near the Aleutian Islands, Alaska. It generated a tsunami which inundated Hilo on the island of Hawai'i with a

surge. The area where the earthquake occurred is where the Pacific Ocean floor is subducting (or being pushed downwards) under Alaska.

Examples of tsunami originating at locations away from convergent boundaries include Storegga about 8,000 years ago, Grand Banks 1929, Papua New Guinea 1998 (Tappin, 2001). The Grand Banks and Papua New Guinea tsunamis came from earthquakes which destabilised sediments, causing them to flow into the ocean and generate a tsunami. They dissipated before traveling transoceanic distances.

The cause of the Storegga sediment failure is unknown. Possibilities include an overloading of the sediments, an earthquake or a release of gas hydrates (methane etc.).

The 1960 Valdivia earthquake (''M''w 9.5) (19:11 hrs UTC), 1964 Alaska earthquake (Mw 9.2), 2004 Indian Ocean earthquake (Mw 9.2) (00:58:53 UTC) and 2011 Tōhoku earthquake (Mw9.0) are recent examples of powerful megathrust earthquakes that generated tsunamis (known as teletsunamis) that can cross entire oceans. Smaller (Mw 4.2) earthquakes in Japan can trigger tsunamis (called local and regional tsunamis) that can only devastate nearby coasts, but can do so in only a few minutes.

### Landslides

In the 1950s, it was discovered that larger tsunamis than had previously been believed possible could be caused by giant submarine landslides. These rapidly displace large water volumes, as energy transfers to the water at a rate faster than the water can absorb. Their existence was confirmed in 1958, when a giant landslide in Lituya Bay, Alaska, caused the highest wave ever recorded, which had a height of 524 metres (over 1700 feet). The wave didn't travel far, as it struck land almost immediately. Two people fishing in the bay were killed, but another boat amazingly managed to ride the wave. Scientists named these waves megatsunami.

's meteotsunamic storm surge over the Bolivar Peninsula in 2008.]] Scientists discovered that extremely large landslides from volcanic island collapses can generate megatsunamis that can cross oceans. <!– comment out pending translation <gallery> File:Tsunami4.JPG|Most tsunamis are caused by submarine earthquakes that dislocate the oceanic crust, pushing water upwards. File:Tsunami3.JPG|Tsunami can be generated by erupting submarine volcanos ejecting magma into the ocean. File:Tsunami5.JPG|A gas bubble erupting in a deep part of the ocean can also trigger a tsunami. </gallery> –>

### Meteotsunamis

Some meteorological conditions, especially deep depressions such as tropical cyclones, can generate a type of storm surge called a meteotsunami which raises water heights above normal levels, often suddenly at the shoreline.<ref name=“Monserrat”>

</ref>

In the case of deep tropical cyclones, this is due to very low atmospheric pressure and inward swirling winds causing an uplifted dome of water to form under and travel in tandem with the storm. When these water domes reach shore, they rear up in shallows and surge laterally like earthquake-generated tsunamis, typically arriving shortly after landfall of the storm's eye.<ref>

</ref><ref>Eyewitness video of Supertyphoon Haiyan's meteotsunamic storm surge on November 6, 2013</ref>

## Characteristics

Tsunamis cause damage by two mechanisms: the smashing force of a wall of water travelling at high speed, and the destructive power of a large volume of water draining off the land and carrying a large amount of debris with it, even with waves that do not appear to be large.

While everyday wind waves have a wavelength (from crest to crest) of about

and a height of roughly

, a tsunami in the deep ocean has a much larger wavelength of up to

. Such a wave travels at well over

, but owing to the enormous wavelength the wave oscillation at any given point takes 20 or 30 minutes to complete a cycle and has an amplitude of only about

.<ref>Earthsci.org, Tsunamis</ref> This makes tsunamis difficult to detect over deep water, where ships are unable to feel their passage.

The reason for the Japanese name “harbour wave” is that sometimes a village's fishermen would sail out, and encounter no unusual waves while out at sea fishing, and come back to land to find their village devastated by a huge wave.

As the tsunami approaches the coast and the waters become shallow, wave shoaling compresses the wave and its speed decreases below

. Its wavelength diminishes to less than

and its amplitude grows enormously. Since the wave still has the same very long period, the tsunami may take minutes to reach full height. Except for the very largest tsunamis, the approaching wave does not break, but rather appears like a fast-moving tidal bore.<ref name=“Walrus”>

</ref> Open bays and coastlines adjacent to very deep water may shape the tsunami further into a step-like wave with a steep-breaking front.

When the tsunami's wave peak reaches the shore, the resulting temporary rise in sea level is termed run up. Run up is measured in metres above a reference sea level.<ref name=“Walrus” /> A large tsunami may feature multiple waves arriving over a period of hours, with significant time between the wave crests. The first wave to reach the shore may not have the highest run up.<ref name=“Tulane”>

</ref>

About 80% of tsunamis occur in the Pacific Ocean, but they are possible wherever there are large bodies of water, including lakes. They are caused by earthquakes, landslides, volcanic explosions, glacier calvings, and bolides.

## Drawback

All waves have a positive and negative peak, i.e. a ridge and a trough. In the case of a propagating wave like a tsunami, either may be the first to arrive. If the first part to arrive at shore is the ridge, a massive breaking wave or sudden flooding will be the first effect noticed on land. However if the first part to arrive is a trough, a drawback will occur as the shoreline recedes dramatically, exposing normally submerged areas. Drawback can exceed hundreds of metres, and people unaware of the danger sometimes remain near the shore to satisfy their curiosity or to collect fish from the exposed seabed.

A typical wave period for a damaging tsunami is about 12 minutes. This means that if the drawback phase is the first part of the wave to arrive, the sea will recede, with areas well below sea level exposed after 3 minutes. During the next 6 minutes the tsunami wave trough builds into a ridge, and during this time the sea is filled in and destruction occurs on land. During the next 6 minutes, the tsunami wave changes from a ridge to a trough, causing flood waters to drain and drawback to occur again. This may sweep victims and debris some distance from land. The process repeats as the next wave arrives.

## Scales of intensity and magnitude

As with earthquakes, several attempts have been made to set up scales of tsunami intensity or magnitude to allow comparison between different events.<ref name=Gusiakov>

</ref>

### Intensity scales

The first scales used routinely to measure the intensity of tsunami were the Sieberg-Ambraseys scale, used in the Mediterranean Sea and the Imamura-Iida intensity scale, used in the Pacific Ocean. The latter scale was modified by Soloviev, who calculated the Tsunami intensity I according to the formula

:$\,\mathit{I} = \frac{1}{2} + \log_{2} \mathit{H}_{av}$

where $\mathit{H}_{av}$ is the average wave height along the nearest coast. This scale, known as the Soloviev-Imamura tsunami intensity scale, is used in the global tsunami catalogues compiled by the NGDC/NOAA<ref>National Geophysical Data Center / (NGDC/WDS) Global Historical Tsunami Database</ref> and the Novosibirsk Tsunami Laboratory as the main parameter for the size of the tsunami.

### Magnitude scales

The first scale that genuinely calculated a magnitude for a tsunami, rather than an intensity at a particular location was the ML scale proposed by Murty & Loomis based on the potential energy.<ref name=Gusiakov/> Difficulties in calculating the potential energy of the tsunami mean that this scale is rarely used. Abe introduced the tsunami magnitude scale $\mathit{M}_{t}$, calculated from,

:$\,\mathit{M}_{t} = {a} \log h + {b} \log R = \mathit{D}$

where h is the maximum tsunami-wave amplitude (in m) measured by a tide gauge at a distance R from the epicentre, a, b and D are constants used to make the Mt scale match as closely as possible with the moment magnitude scale.<ref>

</ref>

## Warnings and predictions

File:TsunamiHazardSign.svg

Drawbacks can serve as a brief warning. People who observe drawback (many survivors report an accompanying sucking sound), can survive only if they immediately run for high ground or seek the upper floors of nearby buildings. In 2004, ten-year old Tilly Smith of Surrey, England, was on Maikhao beach in Phuket, Thailand with her parents and sister, and having learned about tsunamis recently in school, told her family that a tsunami might be imminent. Her parents warned others minutes before the wave arrived, saving dozens of lives. She credited her geography teacher, Andrew Kearney.

In the 2004 Indian Ocean tsunami drawback was not reported on the African coast or any other east-facing coasts that it reached. This was because the wave moved downwards on the eastern side of the fault line and upwards on the western side. The western pulse hit coastal Africa and other western areas.

A tsunami cannot be precisely predicted, even if the magnitude and location of an earthquake is known. Geologists, oceanographers, and seismologists analyse each earthquake and based on many factors may or may not issue a tsunami warning. However, there are some warning signs of an impending tsunami, and automated systems can provide warnings immediately after an earthquake in time to save lives. One of the most successful systems uses bottom pressure sensors, attached to buoys, which constantly monitor the pressure of the overlying water column.

Regions with a high tsunami risk typically use tsunami warning systems to warn the population before the wave reaches land. On the west coast of the United States, which is prone to Pacific Ocean tsunami, warning signs indicate evacuation routes. In Japan, the community is well-educated about earthquakes and tsunamis, and along the Japanese shorelines the tsunami warning signs are reminders of the natural hazards together with a network of warning sirens, typically at the top of the cliff of surroundings hills.<ref name=“Chanson_2010”>

</ref>

The Pacific Tsunami Warning System is based in Honolulu, Hawai{{okina}}i. It monitors Pacific Ocean seismic activity. A sufficiently large earthquake magnitude and other information triggers a tsunami warning. While the subduction zones around the Pacific are seismically active, not all earthquakes generate tsunami. Computers assist in analysing the tsunami risk of every earthquake that occurs in the Pacific Ocean and the adjoining land masses.

<gallery> File:Bamfield Tsunami Hazard Zone sign.jpg|Tsunami hazard sign at Bamfield, British Columbia Image:Kamakura tsunami.jpg|A tsunami warning sign on a seawall in Kamakura, Japan, 2004 Image:The monument to the victims of tsunami.jpg|The monument to the victims of tsunami at Laupahoehoe, Hawaii File:Tsunami Memorial Kanyakumari.JPG|Tsunami memorial in Kanyakumari beach File:Zona de Inundabilidad.jpg|A Tsunami hazard sign (Spanish - English) in Iquique, Chile. Image:Tsunami Evacuation Route signage south of Aberdeen Washington.jpg|Tsunami Evacuation Route signage along U.S. Route 101, in Washington|alt=Photo of evacuation sign </gallery>

As a direct result of the Indian Ocean tsunami, a re-appraisal of the tsunami threat for all coastal areas is being undertaken by national governments and the United Nations Disaster Mitigation Committee. A tsunami warning system is being installed in the Indian Ocean.

s used in the DART tsunami warning system]]

Computer models can predict tsunami arrival, usually within minutes of the arrival time. Bottom pressure sensors relay information in real time. Based on these pressure readings and other seismic information and the seafloor's shape (bathymetry) and coastal topography, the models estimate the amplitude and surge height of the approaching tsunami. All Pacific Rim countries collaborate in the Tsunami Warning System and most regularly practice evacuation and other procedures. In Japan, such preparation is mandatory for government, local authorities, emergency services and the population.

Some zoologists hypothesise that some animal species have an ability to sense subsonic Rayleigh waves from an earthquake or a tsunami. If correct, monitoring their behavior could provide advance warning of earthquakes, tsunami etc. However, the evidence is controversial and is not widely accepted. There are unsubstantiated claims about the Lisbon quake that some animals escaped to higher ground, while many other animals in the same areas drowned. The phenomenon was also noted by media sources in Sri Lanka in the 2004 Indian Ocean earthquake.<ref>

</ref><ref>

</ref> It is possible that certain animals (e.g., elephants) may have heard the sounds of the tsunami as it approached the coast. The elephants' reaction was to move away from the approaching noise. By contrast, some humans went to the shore to investigate and many drowned as a result.

Along the United States west coast, in addition to sirens, warnings are sent on television and radio via the National Weather Service, using the Emergency Alert System.

### Forecast of tsunami attack probability

Kunihiko Shimazaki (University of Tokyo), a member of Earthquake Research committee of The Headquarters for Earthquake Research Promotion of Japanese government, mentioned the plan to public announcement of tsunami attack probability forecast at Japan National Press Club on 12 May 2011. The forecast includes tsunami height, attack area and occurrence probability within 100 years ahead. The forecast would integrate the scientific knowledge of recent interdisciplinarity and aftermath of the 2011 Tōhoku earthquake and tsunami. As the plan, announcement will be available from 2014.<ref>Forecast of earthquake probability is within 30 years ahead, however Tsunami attack probability is much lower than earthquake so that the plan is set to be within 100 years ahead. Yomiuri Shimbun 2011-05-13 ver.13S page 2,

</ref><ref>IndiaTimes Kunihiko Shimazaki speaks during a press conference in Tokyo Thursday, May 12, 2011</ref><ref>

</ref>

## Mitigation

at Tsu, Japan|alt=Photo of seawall with building in background]]

In some tsunami-prone countries earthquake engineering measures have been taken to reduce the damage caused onshore.

Japan, where tsunami science and response measures first began following a disaster in 1896, has produced ever-more elaborate countermeasures and response plans.<ref>

</ref> That country has built many tsunami walls of up to

high to protect populated coastal areas. Other localities have built floodgates of up to

high and channels to redirect the water from incoming tsunami.

However, their effectiveness has been questioned, as tsunami often overtop the barriers. The 2011 Fukushima nuclear disaster was directly triggered by a tsunami that exceeded the height of the plant's sea wall.<ref name=“:18”>Phillip Lipscy, Kenji Kushida, and Trevor Incerti. 2013. “The Fukushima Disaster and Japan’s Nuclear Plant Vulnerability in Comparative Perspective.” Environmental Science and Technology 47 (May), 6082-6088.</ref> The Okushiri, Hokkaidō tsunami which struck Okushiri Island of Hokkaidō within two to five minutes of the earthquake on July 12, 1993 created waves as much as

tall—as high as a 10-story building. The port town of Aonae was completely surrounded by a tsunami wall, but the waves washed right over the wall and destroyed all the wood-framed structures in the area. The wall may have succeeded in slowing down and moderating the height of the tsunami, but it did not prevent major destruction and loss of life.<ref>

</ref> Iwate Prefecture, which is an area at high risk from tsunami, had tsunami barriers walls totalling

long at coastal towns. The 2011 tsunami toppled more than 50% of the walls and caused many damages.<ref>Kyodo Press "Tsunami toppled more than 50% of sea wall in Iwate prefecture" (JA)</ref>

## As a weapon

There have been studies and at least one attempt to create tsunami waves as a weapon. In World War II, the New Zealand Military Forces initiated Project Seal, which attempted to create small tsunamis with explosives in the area of today's Shakespear Regional Park; the attempt failed.<ref name=“PART2-P9”>

</ref>

## References

• In June 2011, the VOA Special English service of the Voice of America broadcast a 15-minute program on tsunamis as part of its weekly Science in the News series. The program included an interview with a NOAA official who oversees the agency's tsunami warning system. A transcript and MP3 of the program, intended for English learners, can be found at The Ever-Present Threat of Tsunamis.
• abelard.org. tsunamis: tsunamis travel fast but not at infinite speed. retrieved March 29, 2005.
• Dudley, Walter C. & Lee, Min (1988: 1st edition) Tsunami! ISBN 0-8248-1125-9 website
• Iwan, W.D., editor, 2006, Summary report of the Great Sumatra Earthquakes and Indian Ocean tsunamis of December 26, 2004 and March 28, 2005: Earthquake Engineering Research Institute, EERI Publication #2006-06, 11 chapters, 100 page summary, plus CD-ROM with complete text and supplementary photographs, EERI Report 2006-06. ISBN 1-932884-19-X website
• Kenneally, Christine (December 30, 2004). “Surviving the Tsunami.” Slate. website
• Lambourne, Helen (March 27, 2005). “Tsunami: Anatomy of a disaster.” BBC News. website
• Macey, Richard (January 1, 2005). “The Big Bang that Triggered A Tragedy,” The Sydney Morning Herald, p 11—quoting Dr Mark Leonard, seismologist at Geoscience Australia.
• Interactive Map of Historical Tsunamis from NOAA's National Geophysical Data Center
• Tappin, D; 2001. Local tsunamis. Geoscientist. 11–8, 4–7.