6.9 Magnitude Earthquake Rattles California Coast

Earthquake

6.9 magnitude earthquake rattles California coast making for an interesting Sunday night. There was also a small temblor that registered at 3.3 magnitude and hit Eureka at 10:04pm The big event struck the town of Eureka at 10:18pm, and although there were no reported injuries or damage over 3,000 people reported feeling rumbling and shaking to the U.S. Geological Survey. According to the USGS the event that triggered the quake occurred about 10 miles beneath the Pacific seabed and 50 miles west off the coast. Monday morning saw 20 aftershocks measuring magnitude 3.5 and higher, but no damage or injuries have been reported from those either. According to the deputy director of the USGS Keith Knudesn, there is a 5 to 10 percent chance of a larger quake occurring nearby in the next week, but only time will tell if it happens.

Eureka is a town that experiences earthquakes regularly, so citizens took it in stride. The event has been described as a big bump followed by about 30 seconds of shaking and rattling. Shelves vibrated and books and keepsakes fell to the floor, but there were no major losses.

Despite the fortuitous lack of injuries of property damage, Knudsen warns that the town got lucky. 6.9 magnitude quakes are fairly rare and very powerful, if the epicenter had been located higher in the Earth’s crust or closer to shore chances are there would have been much deadlier consequences. Earthquakes happen when two edges of the tectonic plates the Earths crust is composed up press together and eventually snap or one edge is pushed over or under the other. The vibrations come from the accumulated pressure being released by the plates falling into their new positions. After a 6.9 magnitude earthquake rattles the California coast, aftershocks are a given, and the possibility of a second larger quake is very real indeed.

Despite the area being frequently shaken by earthquakes only 10 have been more than a level 6 magnitude since 1980. In 1992 a 7.2 magnitude quake struck Eureka and caused injuries to 95 citizens and tens of millions of dollars’ worth of damage. It was followed by 6.5 and later a 6.7 magnitude aftershock which both caused considerable additional damage before the town could properly respond to the initial shake.

Luckily in this instance no further quakes have yet occurred, and there is no chance of a tsunami due to the depth of the epicenter and the manner in which the tectonic plates shifted. Often a tsunami will occur when the edges of plates drop or rise sharply, causing a large displacement of sea water that rushes in or out of the affected area causing a wave.

The earthquake was felt as far away as San Fransisco, 270 miles south-east of Eureka’s main population center of 27,000 people. Ironically, the areas predisposition to common earthquakes makes the likelihood of a very large event unlikely. Due to the need for immense pressure between the plates, when they slip more often the build-up is less intense, resulting in a smaller quake. But after a 6.9 magnitude earthquake rattles the California coast, hearing that small frequent quakes are the best option is likely small comfort.

By Daniel O’Brien

Sources

Chron
SFGate
Visalia Times-Delta

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