Cascadia's Fault - Jerry Thompson [125]
While this sounded like an infinitesimally small thing to measure, Lindh pointed out that if the coming quake had been a magnitude 7 instead of a 6, then the amount of strain—and the creep along the fault—would probably have scaled up by a factor of ten, which “would be easily observable with current downhole instrumentation.” His point was that new state-of-the-art strainmeters can detect things even those magical GPS rigs cannot see from above.
When a fault creeps way down deep, not all the horizontal motion is transferred to the surface because rocks bend and deform under stress. Therefore, if the rocks started to move hundreds of feet below ground, and if this turned out to be a reliable symptom of a coming rupture, the GPS stations up at the surface might not detect the signal even at the supposed magnitude 7 level. But the much more sensitive strainmeters could—or might.
Lindh took the opportunity to bite back at critics of prediction and those in government committees, labs, and universities who had unofficially given up trying to solve the problem. He ridiculed the fashion in California of making “probability forecasts” so vague that the results were “no longer accurate enough” to be of use to society. For example, the official Working Group on California Earthquake Probabilities has estimated the odds of at least one magnitude 6.7 or larger event in the San Francisco region sometime in the next thirty years to be 62 percent. The odds are 67 percent for the same size jolt to hit the Los Angeles area. But sometime in the next thirty years? How should people respond to a prediction like that? Building codes and insurance rates might be adjusted, but how do the rest of us make sense of it?
The numbers could mean anything or nothing to the majority of citizens, who don’t really comprehend statistical probabilities. Instead Lindh argued that the data collected at Parkfield and elsewhere in recent years had vastly improved our understanding of fault behavior, of the accumulation of strain, and of seismic patterns over longer periods so that it should be possible now to target the three most likely zones to rupture and to design more focused “prediction experiments” that could save lives.
“While I understand that some in the field of seismology are afraid of the ‘P word,’ the public is not,” wrote Lindh. “They think it’s what seismologists are working on. It is my opinion that the public would respond very positively to our highlighting some of the most serious threats to their lives and welfare, particularly if it were accompanied by a serious commitment to do everything we could to further our understanding of those segments, and maybe in the process even reduce the risk they represent.”
Prediction fell from grace with a disappointing thud just as Kazushige Obara in Japan and Herb Dragert and Garry Rogers at the Geological Survey of Canada were learning about ETS (episodic tremor and slip), the bizarrely regular twitching deep down on the lower reaches of the Cascadia Subduction Zone that promised a new way to track the behavior of a major fault. At roughly the same time in California, all that high-tech equipment buried in the ground or stretched across the San Andreas at Parkfield—the creepmeters, the tiltmeters, the seismographs, and lasers—was being reconfigured for a new and bigger experiment. The desire to know more about what happens along the rocky surfaces of a fracture zone just before an earthquake was actually gaining momentum despite the alleged failure of the Parkfield prediction.
Parkfield was reborn as SAFOD—the San Andreas Fault Observatory at Depth, a deep-earth research project funded by the National Science Foundation in partnership with the USGS. In June 2004 an oil rig crew started drilling a hole into the hilly brown rangeland not far from the initiating point of the 1966 Parkfield