INTRODUCTION TO SEISMIC MONITORING Relevance and Rationale for Monitoring

Although earthquakes happen frequently in many parts of the world, any occurrence of a moderate to large event is sudden and unexpected. Thus, the earthquake process can be interesting and even frightening to people. Most earthquakes are associated with natural, dynamic processes that shape Earth’s landscape. The vast majority of earthquakes are caused by sudden slip along faults, resulting in seismic waves that shake the ground, often with suffi cient force to damage structures or trigger other events, such as landslides. When signifi cant earthquakes occur anywhere in the world, such as the December 2004 tsunami-generating event in Indonesia that killed more than 200,000 people, or the October 2005 earthquake in Pakistan that killed more than 70,000 people, emergency response and relief efforts come from around the globe, and there is renewed interest in understanding the causes and in mitigating the devastating effects of earthquakes. Earthquakes can be signifi cant hazards, as evidenced by occasional damaging and deadly events. Individuals, governments, and organizations can respond to the hazard by understanding the probability and the likely effects of signifi cant events; preparing emergency response plans; enhancing public knowledge about what to do in case of an earthquake; and taking specifi c steps (such as reinforcing critical or weak structures) to reduce the risk of earthquakes.