1999 Hector Mine earthquake
The 1999 Hector Mine earthquake occurred in Southern California, United States, on October 16 at 02:46:50 PDT. Its moment magnitude was 7.1 and the earthquake was preceded by 12 foreshocks, the largest of which had a magnitude of 3.8. The event is thought to have been triggered by the 1992 Landers earthquake which occurred seven years earlier. It also deformed nearby faults vertically and horizontally. The earthquake's hypocenter was at a depth of 20 kilometers and its epicenter at 34.603° N 116.265° W. The earthquake caused minimal damage and no fatalities due to the distance of its epicenter from populated centers. The significance of this earthquake lies in the fact that, firstly, it had a relatively-high magnitude but caused little damage and secondly, it offered more evidence that stress accumulation over time causes earthquakes. Precursor events It is thought that the 1999 Hector Mine earthquake may have been triggered by the 1992 Landers earthquake seven years prior, since the recurrence interval of large earthquakes in the Eastern California Shear Zone is considered to be in the order of thousands of years. That event had a magnitude of 7.3, similar to the Hector Mine quake, was also a strike slip event. Another reason why the Landers earthquake is likely to have triggered the Hector Mine earthquake as they both occurred 20 kilometers apart. The Hector Mine earthquake is thought to be an example of increased fault stress from a separate quake which built over seven years until finally rupturing in 1999. As a result, studying of the Landers earthquake became quite important in understanding this new earthquake near the turn of the century. Foreshocks During a fault rupture, stress is released as two sides of fault slip and move past each other. Stress can be transferred from one fault to adjacent faults, causing subsequent fault ruptures. By nature, foreshocks are not possible to identify as such until after the main shock or largest magnitude of shaking occurs. For this reason, they can not be used to predict larger earthquakes or give warnings to residents of the affected area. That being said, it was determined after the fact that a sequence of twelve foreshocks preceded the Hector Mine main shock. These foreshocks progressed northward 20 hours before the mainshock, and occurred in the same location as a cluster of off-fault aftershocks of the 1992 Landers earthquake. The largest of the twelve foreshocks had a magnitude of 3.8 and occurred at 7:41 PM PDT on the 15th of October. Earthquake This strike-slip earthquake occurred in a remote part of the Mojave Desert, east-southeast of Barstow, California, inside the Twentynine Palms Marine Corps Base. Strike-slip faults are fractures where the blocks have mostly moved horizontally. If the block under the right foot of the observer straddling the fault moves towards the observer, the slip style is termed right lateral; if the block under the observer's left foot moves towards the observer, the fault is termed left lateral. This right-lateral strike-slip quake involved rupturing the