Building devastation from the 2008 Wenchuan earthquake in China 4

Building devastation from the 2008 Wenchuan earthquake in China 4 Earthquake Prediction and Predictability

“When will the Big One be?” is the primary question asked of seismologists by the public. Most people asking this question are seeking accurate predictions of earthquake magnitude, location, and time with a high probability of occurrence, such as “there will be a magnitude 7.0 earthquake beneath San Francisco on Wednesday at noon.” Confronting the enigma of earthquake prediction has been a challenge to seismology since the emergence of the discipline.

There are two approaches to this problem. The first is the “silver bullet” approach that seeks an unambiguous earthquake precursory signal. The ideal signal would be detectable before all earthquakes. Unfortunately, no such universal precursory signal has yet been identified. There may instead be precursory signals that precede only some earthquakes, and only in specific environments. Candidates include increased seismicity and crustal strain, changes in seismic velocities near a fault, variations in electrical resistivity and potential, radio frequency emission, and changes in ground-water levels and chemistry. These observations are worthy of further research efforts once it has been demonstrated that a specific observation made before an earthquake is unique to the time window before the earthquake. It should be noted that many reported precursory signals have not passed even this basic requirement.

The second approach is to develop an understanding of the complete physical system responsible for earthquakes. Earthquakes involve processes occurring at multiple spatial and temporal scales for which direct observations are severely limited.Much progress has been made understanding crustal deformation, stress accumulation, fault interaction, and rupture dynamics, but the challenge remains to link these processes to the underlying physics of fault rupture. It is also valuable to improve our understanding of patterns of seismicity using high-precision earthquake catalogs that are now being produced by advanced methodologies. Working toward a deterministic understanding of precise earthquake catalogs may reveal many currently hidden aspects of the earthquake system. Studying the basic physical processes of earthquakes and catalogs over longer time periods will reveal whether aspects of the complex earthquake system are intrinsically predictable or not, and what observations may yield the best prospects of providing some predictive capabilities.

The complexity of the earthquake process, and intrinsic observational limitations, may make earthquake rupture a fundamentally unpredictable phenomenon. Even if earthquakes could be predicted with a high degree of probability and accuracy, this would solve only part of society’s earthquake problem. The fate of New Orleans after Hurricane Katrina illustrates that even when imminent disaster is predicted several days in advance, there can still be terrible outcomes due to inadequate preparedness prior to an inevitable event. If not built to withstand earthquakes, then homes and livelihoods will still be destroyed. It is thus critical to continue to have a sustained commitment to improving scientifically informed earthquake engineering and mitigation efforts regardless of whether some level of earthquake predictability is ever achieved.


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