| The Textbook Earthquake | |
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Geologists rode along with the soldiers and documented what had happened. One key piece of information they wanted was the coseismic slip—the amount of movement along the fault that the earthquake caused. They moved very carefully, because the ground was littered with craters and unexploded bombs. In places the ground was thrown up in hummocks; in other places fissures yawned. The coming winter's flash floods and military exercises would wipe out much of this data.
A few days later, a satellite of the European Space Agency took a fresh radar image of the region. Combining that image with one taken five weeks before, a group of geophysicists at the University of California San Diego created a large-scale image that mapped the regional seismic displacement. It also showed that the quake (by now given the name of the abandoned Hector Mine near the epicenter) had triggered movement on nearby faults. It was put on the Web within a day of acquiring the satellite image, and two weeks later the group submitted a paper to Geophysical Research Letters.
By then, the U.S. Geological Survey had issued a report and erected a whole special Web site, full of fresh information, databases, and links. A public information effort of this scale and speed had never been done before, but in the future the USGS made it routine.
Scientifically, the interesting thing about the Hector Mine quake is that it began in an area where the Landers earthquake of 28 June 1992 had increased stress in the Earth's crust. A similar area of increased stress occurred on the other side of the Landers quake—on the great San Andreas fault system. According to modeling done at the University of Nevada Reno, the Hector Mine quake seems to have added further to that stress. Here's more on the stress triggering hypothesis, which looks better every year.
Click the thumbnails for bigger pictures.
In places there was five meters of displacement, as judged from the way that dirt roads, gravel streaks, gullies, and other desert landforms had been disturbed.
Did you feel it? The USGS Hector Mine Web site has built a shake map from public reports of how it felt. That's another thing that was once laborious but is now easy on the Web. Read more about the program.
See my Hector Mine quake page for more links.
