In New Zealand, Vere-Jones et al. (1998) proposed that we combine our probabilistic forecasting based on slip rates and estimated return times of earthquakes with the search for earthquake precursors. Geller (1997) has discounted the possibility that earthquakes telegraph their punches, and up to now, the Americans and Japanese have failed to find a “magic bullet” precursor that gives us a warning reliable enough that society can benefit. Yet precursors, notably earthquake foreshocks, gave advance warnings of earthquakes in China and Greece.
Possible precursors now under investigation include patterns in seismicity (such as foreshocks but in other instances a cessation of small earthquakes), changes in the fluid level of water wells, rapid changes in crustal deformation as measured by permanent GPS stations, anomalous electrical and magnetic signals from the Earth, faults being stressed by adjacent faults that recently ruptured in an earthquake, even the effects of Earth tides. For this method to be successful, massive amounts of data must be analyzed by high-speed computers, so that real-time data can be compared quickly with other past data sets where the outcome is known. A single precursor might not raise an alarm, but several at the same time might lead to an alert. The mistake made by previous scientific predictors, including the Chinese, was to put too much dependence on a single precursor and an unrealistic view of how reliable that precursor would be in predicting the time, location, and magnitude of a forthcoming earthquake.
In the future, we could see earthquake warning maps pointing out an increased risk beyond that based on earthquake history, analogous to maps showing weather conditions favorable to tornadoes, hurricanes, or wildfires. The TV seismologist or geologist could become as familiar as the TV meteorologist. If an earthquake warning were issued in this way, the public would be much better prepared than they would be if no warning had been issued, and there would be no panic, no fleeing for the exits. If no earthquake followed, the social impact would not be great, although local residents would surely be grousing about how the earthquake guys couldn’t get it right. But they would be alive to complain.
Although we do not have a regional system in place, the USGS maintains an alert system at Parkfield on the San Andreas Fault and at Mammoth Lakes in the eastern Sierra, where volcanic hazard is present in addition to earthquake hazard. Unusual phenomena at either of these places are evaluated and reported to the public. Pierce County, Washington, has established an alert system for possible mudflows from Mount Rainier (Figure 6-1). The monitoring system for metropolitan Los Angeles and the San Francisco Bay Area is becoming sophisticated enough that anomalous patterns of seismicity or other phenomena would be noticed by scientists and pointed out to the public. Indeed, the Lake Elsman earthquakes of 1988 and 1989, prior to the Loma Prieta earthquake, were reported to the Office of Emergency Services, and alerts were issued. There are plans to extend this capability to cities of the Northwest.