OhioSeis Network must determine basic earthquake parameters:
- Hypocenter parameters: Epicenter, depth, and origin time (Depends on regional velocity structure).
- Magnitude: requires reliable wave amplitudes and correction factors
Then, we can study enhanced characteristics such as Focal Mechanisms and Quarry Blast discrimination, and so on.
Focus on Magnitude
Basic definition of magnitude
In the central and eastern North America, Lg becomes the dominant phase
What is Lg?
Lg is a complex surface waves that grows from the Sg phase.
What does Lg look like?
A distinct high-amplitude phase with U=3.5 km/sec, easily seen at distances of hundreds of km from earthquakes with M>5.
What do Ohio Earthquakes look like at regional distances?
We see an unusual regionally coherent "local Lg" wave with U<2.0 km/sec that is a distinct large wave at even small distances.
So what should we do to calculate the Ohio earthquakes magnitude?
We must find a consistent wave arrival and procedure (see below). Meanwhile, we are using the "LLg" wave and Hermann and Kijko (1983) formula.
Amplitude Study of recent
Ohio and Michigan earthquakes
Goal: To find the best combination of a large amplitude wave that is also regionally consistent so that a reliable magnitude can be assigned to local earthquakes — large and small.
Issues involved in practical aspects of wave amplitude and magnitude
- Amplitudes in frequency domain
- Anti-aliasing filter
- Use wave amplitudes at Nyquist frequency?
Manipulation of the MN formula suitable for broad-band velocity instruments
The 2001.01.26 Ashtabula OH earthquake
The 2000.08.07 Alliance OH earthquake
The 2001.10.23 Calhoun Co. MI earthquake
Conclusions and Recommendations
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