Recent Developments in Earthquake Hazards Studies

Abstract

In recent years, there has been great progress understanding theunderlying causes of earthquakes, as well as forecasting theiroccurrence and preparing communities for their damaging effects. Platetectonic theory explains the occurrence of earthquakes at discrete plateboundaries, such as subduction zones and transform faults, but diffuseplate boundaries are also common. Seismic hazards are distributed over abroad region within diffuse plate boundaries. lntraplate earthquakesoccur in otherwise stable crust located far away from any plateboundary, and can cause great loss of life and property. Theseearthquakes cannot be explained by classical plate tectonics, and assuch, are a topic of great scientific debate. Earthquake hazards aredetermined by a number of factors, among which the earthquake magnitudeis only one factor. Other critical factors include population density,the potential for secondary hazards, such as fire, landslides andtsunamis, and the vulnerability of man-made structures to severe strongground motion. In order to reduce earthquake hazards, engineers andscientists are taking advantage of new technologies to advance thefields of earthquake forecasting and mitigation. Seismicity iseffectively monitored in many regions with regional networks, and worldseismicity is monitored by the Global Seismic Network that consists ofmore than 150 high-quality, broadband seismic stations using satellitetelemetry systems. Global Positioning Satellite (GPS) systems monitorcrustal strain in tectonically active and intraplate regions. Arelatively recent technology, Interferometric Synthetic Aperture Radar(InSAR) uses radar waves emitted from satellites to map the Earth'ssurface at high (sub-cm) resolution. InSAR technology opens the door tocontinuous monitoring of crustal deformation within active plateboundaries. The U.S. Geological Survey (USGS), along with otherpartners, has created Shake Map, an online notification system thatprovides near-real-time post-earthquake maps of ground shakingintensity. These maps are especially useful for the coordination ofemergency response teams and for the improvement of building codes.Using a combination of these new technologies, with paleoseismologystudies, we have steadily improved the science of earthquake forecastingwhereby one estimates the probability that an earthquake will occurduring a specified time interval. A very recent development isEarthquake Early Warning, a system that will provide earthquakeinformation within seconds of the initial rupture of a fault. Thesesystems will give the public some tens of seconds to prepare forimminent earthquake strong ground motion. Advances in earthquake sciencehold the promise of diminishing earthquake hazards on a global scaledespite ever-increasing population growth.