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Saturday, May 07, 2016

Earthquakes: Locked and Loaded

By Douglas V. Gibbs

The Western United States, from Seattle to San Diego, is ready to start rumbling.

According to the United States Geological Service, near Mount St. Helens there has been small magnitude earthquake swarms.
From USGS:  Beginning March 14, 2016, a number of small magnitude earthquakes have occurred beneath Mount St. Helens, at a depth between 2 and 7 km (1.2 to 4 miles). Over the last 8 weeks, there have been over 130 earthquakes formally located by the Pacific Northwest Seismic Network and many more earthquakes too small to be located. The earthquakes have low magnitudes of 0.5 or less; the largest a magnitude 1.3. Earthquake rates have been steadily increasing since March, reaching nearly 40 located earthquakes per week. These earthquakes are too small to be felt at the surface.
The earthquakes are volcano-tectonic in nature, indicative of a slip on a small fault. Such events are commonly seen in active hydrothermal and magmatic systems. The magma chamber is likely imparting its own stresses on the crust around and above it, as the system slowly recharges. The stress drives fluids through cracks, producing the small quakes. The current pattern of seismicity is similar to swarms seen at Mount St. Helens in 2013 and 2014; recharge swarms in the 1990s had much higher earthquake rates and energy release.
No anomalous gases, increases in ground inflation or shallow seismicity have been detected with this swarm, and there are no signs of an imminent eruption. As was observed at Mount St. Helens between 1987-2004, recharge can continue for many years beneath a volcano without an eruption.For more information, see the Activity Updates for Volcanoes in CVO Area of Responsibility and Earthquake Monitoring at Mount St. Helens.
The Los Angeles Times reveals in its own article that down in California the "San Andreas fault [is] 'locked, loaded and ready to roll' with [a] big earthquake."

Growing up in Southern California, the fear of the next "big one" has always been present.  Hollywood helped remind us that a catastrophic earthquake is on the horizon, first with its massive production "Earthquake" in 1974, and recently with "San Andreas" in 2015.  An earthquake theme also remains in place during part of the tram ride at Universal Studios.

Small earthquakes are so common, and a part of the landscape in California, that West Coast residents largely shrug them off as being a part of living where the weather is great.  Many Californians are prepared, even putting preppers to shame with how prepared we are for The Big One.  However, most Californians are not prepared, placing them in a position of being a statistic when the next big earthquake hits.  In addition to questions regarding our preparedness for the next big quake, even with all of the new retrofits in buildings and freeways, when the Big One arrives it will be devastating in loss of lives, and the cost to rebuild.

Recently, a leading earthquake scientist said that California is long overdue for a large earthquake, and he said that Southern California’s section of the San Andreas fault is “locked, loaded and ready to roll.”

San Andreas is California's longest fault.  The southern section of the San Andreas fault has not had a tension-relieving large earthquake since 1857, when a magnitude 7.9 earthquake ruptured from Monterey County and the San Gabriel Mountains near Los Angeles.

We are a part of the ring of fire, as the State of Washington is all too aware.  Also, in terms of tectonics, the Pacific plate is moving northwest relative to North America at about 16 feet, or 5 meters, every 100 years.  That is a need of relief of about 16 feet every 100 years.  With the southern San Andreas fault quiet for more than a century, the conclusion is simple - we are long overdue.

The earthquake scientist mentioned above, Thomas Jordan, director of the Southern California Earthquake Center, recently gave a keynote address at the National Earthquake Conference in Long Beach.  In his talk he said, “The springs on the San Andreas system have been wound very, very tight. And the southern San Andreas fault, in particular, looks like it’s locked, loaded and ready to go.”

Various sections in Southern California have been waiting even longer for a good release through earthquake rumbling.  In San Bernardino County, the fault has not moved substantially since an earthquake in 1812, and further southeast toward the Salton Sea, it has been relatively quiet since about 1680 to 1690.

According to a 2008 U.S. Geological Survey report, an earthquake with the magnitude of 7.8 on the southern San Andreas fault would cause more than 1,800 deaths, 50,000 injuries, $200 billion in damage and severe, long-lasting disruptions. Among the predicted problems: The sewer system could be out of commission for six months.

Wow, that's a lot of crap we are going to have to deal with.

The shaking of the next Big One could be as short as one minute, or could last for two to three minutes - a time period that seems relatively short on the surface, but during an earthquake, a few minutes can seem like a lifetime.

The strongest impact in terms of shaking from a large earthquake in Southern California would be in the Coachella Valley, Inland Empire and Antelope Valley due east and southeast of Los Angeles.  Scientists also warn that an earthquake that size could send pockets of strong shaking into areas where sediments trap shaking waves, such as the San Gabriel Valley and East Los Angeles.

The potential to how devastating a large earthquake can be has been determined by studying the last large earthquake, an 1857 temblor, which was an estimated magnitude of 7.9.  The earthquake began in Monterey County, sending its wave of devastation south near the northern edge of Los Angeles County, then east toward the Cajon Pass in San Bernardino County.

The quake was so powerful that the soil liquefied, causing trees as far away as Stockton to sink. Trees were also uprooted west of Fort Tejon. The shaking lasted 1 to 3 minutes.

The San Andreas fault travels east of Los Angeles, 30 miles away from downtown.  Still, the city would receive heavy shaking from a Big One.

With our current technology, computer generated simulations help today's scientists imagine what a potential big quake would do in the terms of rocking, and damage.  According to the simulations, the shaking spreads out, expanding as the wave forces its way down the faultline, sending pockets of shaking into the Los Angeles region that persist for long periods of time.

One wonders if we are entering a period of great trembling, where earthquakes in various places will become commonplace.

-- Political Pistachio Conservative News and Commentary

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