According to the GEOFOrschungsNetzwerk (Geosciences Research Network – GEOFON), an infrastructure of the Deutsches GeoForschungsZentrum (German Research Centre for Geosciences – GFZ) in Potsdam, the epicentre was only a few kilometres away from the Napa Valley wine-growing area and about 70 kilometres northeast of the city of San Francisco. The event occurred on Sunday, August 24, 2014 at 3:20 am local time (12:20 pm German time) at a depth of some ten kilometres.

California has been repeatedly affected by strong earthquakes. The last strong earthquake with a magnitude of 6.9 occurred there in 1989. San Francisco is located on the San Andreas Fault, a transform fault with a length of more than 1,000 kilometres, where the Pacific Plate slides northwards and the North American Plate southwards and the two plates rub against each other.

Violent earthquakes also in Chile and Peru

On April 2 this year,  a magnitude 8.1 earthquake occurred near the village of Pisagua, north of Iquique, the largest in Chile since 2010, when an event with magnitude 8.8 occurred several 100 km further south, in central Chile. On the west coast of South America, the Pacific Nazca Plate subducts beneath the continent and builds up stress, which is released in earthquakes.

A further violent tremor of magnitude 6.8 occurred on Sunday in Peru at a depth of 89 km, much deeper than most earthquakes. The subduction of the Nazca Plate beneath the South American Plate is also responsible for this earthquake, as with the earthquake on Saturday (August 23) in Chile. However, unlike the above-mentioned earthquakes in Chile the quake did not take place on the plate boundary  but within the subducting oceanic Nazca Plate. The requisite stresses are built up by internal deformation of the plate.

GEOFON is part of the Modular Earth Science Infrastructure (MESI) of the GFZ and offers various services in the "Global Networks", "Data Archiving and Distribution" and "Data Communication" area. It supports the Helmholtz mission by offering seismological infrastructure for studying the complex Earth system and contributing to the major challenge of reducing earthquake and tsunami hazards.

By clicking on the map you will see earthquake parameters such as the epicentre, in other words the location at which the event has taken place. The depth, magnitude and origin time (UTC – Coordinated Universal Time) of the earthquake are also shown.  Very large earthquakes can have rupture zones extending over tens or even hundreds of kilometres and for these earthquakes the shown location indicates the point, at which the earthquake rupture started.

Text: Karl Dzuba, Earth System Knowledge Platform