California's Earthquakes and What Can Be Expected in Years To Come

With all the recent earthquake activity around the world, scientists have started to focus on California, USA. The scientists have determined California will have many earthquakes with a magnitude of 6.7 or greater over the next 30 years. Earthquakes of this magnitude can be very deadly. In 1989, Loma Prieta had an earthquake with a magnitude of 6.9 and in Northridge in 1994 had an earthquake of 6.7 and these two earthquakes showed how deadly an earthquake can be. Scientists who have been studying the possibility of an earthquake occurring in southern California say the quake is likely to be a 7.5 or greater. Building codes, earthquake insurance, and emergency planning will be affected by these new results, which highlight the urgency to prepare now for the powerful quakes that are inevitable in California's future.


Earthquake forecasts for California have been developed in the past by multidisciplinary groups of scientists and engineers, each known as a "Working Group on California Earthquake Probabilities" (WGCEP 1988, 1990, 1995, 2003). Organizations sponsoring WGCEP 2007 include the USGS, California Geological Survey, and the Southern California Earthquake Center. The comprehensive new forecast builds on previous studies and also incorporates abundant new data and improved scientific understanding of earthquakes.


Earthquakes occur when a fault line raptures (when the crack in the Earth's crust gives away and slips under tectonic pressure) and seismic waves (are caused by the sudden fault motion). Seismic waves branch out like ripples from a pebble tossed into a pond. These seismic waves cause the most damage. The quake's magnitude determines the strength of the waves. The UCERF study's goal was to determine probabilities for different parts of California of earthquake ruptures of various magnitudes, but not to estimate the likelihood of shaking ("seismic hazard") that will be caused by these quakes. This distinction is important, because even areas in the State with a low probability of fault rupture can experience shaking and damage from distant, powerful quakes.


California straddles the boundary between two of the Earth's tectonic plates. As a result, California is broken up by numerous earthquake faults. Taking into account the earthquake histories and relative rates of motion on these many faults. There is a 46% chance for one or more powerful quakes of magnitude 7.5 or greater. A quake is twice as likely to occur in the southern half of the State as in the northern half by 37% to 15%. Smaller magnitude earthquakes are more frequent than larger quakes. According to the new forecast, about 3 magnitudes that are a magnitude of 5 or greater will occur in the California region per year. Earthquakes at a magnitude of 6 or greater will occur about every 1.5 years.


California is not the only area to be on alert for deadly earthquakes. There are many locations over the world that has seismic activity. Afghanistan has had 5 earthquakes with a magnitude of 6.5 or greater, Argentina had an 8.5 earthquake in 1922, Caucasia lost 80,000 people to an earthquake in 1667, China had a size 8 earthquake and lost 830,000 people, and with the largest earthquake in the world, Chile had a 9.5 magnitude in 1960. The 9.5 magnitude quake killed 1,655, 3,000 were injured and 2,000,000 were left homeless. The quake caused a tsunami that killed a total of over 5,700 people and did $75 million damage in Hawaii, $50 million damage in Japan and $500,000 damage to the west coast of the United States (https://www.usgs.gov/).