Earthquakes — LLMpedia

Earthquakes
Name	Earthquake
Caption	Seismic waves recorded by a seismograph

Contents

Earthquakes are sudden releases of energy in the Earth's lithosphere that produce seismic waves and ground shaking, often occurring along fault zones associated with plate boundaries and intraplate regions. Major earthquakes have shaped the histories of San Francisco, Lisbon, Tokyo, Istanbul, and Naples, and have driven developments in United States Geological Survey, Japan Meteorological Agency, European-Mediterranean Seismological Centre, International Seismological Centre, and Centers for Disease Control and Prevention approaches to hazard management. Scientific study of earthquakes has involved figures and institutions such as Charles Richter, Beno Gutenberg, Andrija Mohorovičić, Kiyoo Mogi, and Harry Fielding Reid and has influenced projects like Global Seismographic Network, USGS ShakeMap, Seismic Hazard Assessment, and International Decade for Natural Disaster Reduction.

Introduction

Earthquakes occur where stress accumulation in the Earth's crust or mantle exceeds the strength of rocks, producing rupture and seismic radiation that is recorded by seismometers at observatories such as Caltech Seismological Laboratory, Incorporated Research Institutions for Seismology, Observatoire Volcanologique et Sismologique de Guadeloupe, and Seismological Society of America. The global distribution of seismicity correlates with plate boundaries identified by Alfred Wegener, Harry Hess, John Tuzo Wilson, and mapped by initiatives like Scripps Institution of Oceanography and Lamont–Doherty Earth Observatory. Historical catalogues compiled by NOAA, British Geological Survey, Geological Survey of Japan, and Chinese Academy of Sciences document impacts on cities such as Mexico City, Kobe, Christchurch, and Port-au-Prince.

Most large earthquakes are generated by slip on faults linked to major tectonic settings including transform boundaries exemplified by the San Andreas Fault, convergent zones like the Andes and Japan Trench, and divergent ridges such as the Mid-Atlantic Ridge. Mechanisms involve elastic rebound theory developed by Harry Fielding Reid, subduction processes studied near Aleutian Islands and Sumatra, and crustal deformation observed in regions like Himalayas and East African Rift. Intracontinental events occur in cratons monitored by United States Geological Survey records and were studied after events near New Madrid, Kashmir, and Guangzhou; induced seismicity related to projects by Chevron, ExxonMobil, and Enel has occurred near Paradox Valley and Pohang.

Seismographs and accelerometers at facilities run by USGS, Japan Meteorological Agency, European-Mediterranean Seismological Centre, and Global Seismographic Network record waveforms used to compute scales such as the Richter magnitude scale, moment magnitude scale, and intensity scales like the Modified Mercalli intensity scale. Signal processing and tomography methods developed at Massachusetts Institute of Technology, University of Tokyo, and California Institute of Technology resolve hypocenter depth and focal mechanisms, while repositories such as International Seismological Centre and Incorporated Research Institutions for Seismology archive waveform data. Rapid magnitude estimates inform products like USGS PAGER and notifications used by Federal Emergency Management Agency, Civil Protection Department (Italy), and National Disaster Management Authority (India).

Primary hazards include ground shaking, surface rupture, and fault propagation that damage infrastructure in urban areas such as Los Angeles, Tehran, Mexico City, and Jakarta; secondary hazards include tsunamis generated along subduction zones like the 2011 Tōhoku earthquake and tsunami source region near Honshu and the 2004 Indian Ocean earthquake and tsunami source near Sumatra. Earthquakes can trigger landslides in regions like the Himalayas and Andes, liquefaction in sedimentary basins such as Tokyo Bay and San Francisco Bay, and cascading failures affecting dams overseen by agencies like US Army Corps of Engineers and Istituto Superiore per la Protezione e la Ricerca Ambientale. Economic and social impacts have been documented after events in Haiti, Chile, Nepal, and California.

Long-term forecasting and seismic hazard mapping produced by USGS, Geological Survey of Japan, National Research Council (US), and UN Office for Disaster Risk Reduction use paleoseismology, geodesy from GPS, and paleotsunami deposits studied by Woods Hole Oceanographic Institution and National Oceanography Centre. Short-term prediction remains elusive despite studies involving statistical models from Reasenberg and Jones and prospective testing in collaborations with International Association of Seismology and Physics of the Earth's Interior. Early warning systems deployed by Japan Meteorological Agency, Mexican Seismic Alert System, ShakeAlert, and Taiwan Central Weather Administration use dense sensor networks to provide seconds-to-minutes of warning to utilities like Tokyo Electric Power Company, transit operators in New York City, and hospitals such as Cedars-Sinai Medical Center.

Mitigation relies on building codes and standards issued by agencies like International Code Council, Eurocode, Japan Building Standards Law, and national authorities such as Federal Emergency Management Agency and Ministry of Land, Infrastructure, Transport and Tourism (Japan), retrofitting programs in cities like San Francisco and Istanbul, and land-use planning informed by hazard maps from USGS and British Geological Survey. Preparedness includes public education campaigns by Red Cross, UNICEF, and World Health Organization, continuity planning by companies such as AT&T and Bank of America, emergency response engineering by National Guard (United States) units, and community drills modeled after exercises in New Zealand, Chile, and Japan.