Recent Developments in Earthquake Hazards Studies

In recent years, there has been great progress understanding the underlying causes of earthquakes, as well as forecasting their occurrence and preparing communities for their damaging effects. Plate tectonic theory explains the occurrence of earthquakes at discrete plate boundaries, such as subduction zones and transform faults, but diffuse plate boundaries are also common. Seismic hazards are distributed over a broad region within diffuse plate boundaries. Intraplate earthquakes occur in otherwise stable crust located far away from any plate boundary, and can cause great loss of life and property. These earthquakes cannot be explained by classical plate tectonics, and as such, are a topic of great scientific debate. Earthquake hazards are determined by a number of factors, among which the earthquake magnitude is only one factor. Other critical factors include population density, the potential for secondary hazards, such as fire, landslides and tsunamis, and the vulnerability of man-made structures to severe strong ground motion. In order to reduce earthquake hazards, engineers and scientists are taking advantage of new technologies to advance the fields of earthquake forecasting and mitigation. Seismicity is effectively monitored in many regions with regional networks, and world seismicity is monitored by the Global Seismic Network that consists of more than 150 high-quality, broadband seismic stations using satellite telemetry systems. Global Positioning Satellite (GPS) systems monitor crustal strain in tectonically active and intraplate regions. A relatively recent technology, Interferometric Synthetic Aperture Radar (InSAR) uses radar waves emitted from satellites to map the Earth’s surface at high (sub-cm) resolution. InSAR technology opens the door to continuous monitoring of crustal deformation within active plate boundaries. The U.S. Geological Survey (USGS), along with other partners, has created ShakeMap, an online notification system that provides near-real-time post-earthquake maps of ground shaking intensity. These maps are especially useful for the coordination of emergency response teams and for the improvement of building codes. Using a combination of these new technologies, with paleoseismology studies, we have steadily improved the science of earthquake forecasting whereby one estimates the probability that an earthquake will occur during a specified time interval. A very recent development is Earthquake Early Warning, a system that will provide earthquake information within seconds of the initial rupture of a fault. These systems will give the public some tens of seconds to prepare for imminent earthquake strong ground motion. Advances in earthquake science hold the promise of diminishing earthquake hazards on a global scale despite ever-increasing population growth.