Elaine Meinel Supkis
Two more earthquakes greater than 4 mag hit the lower end of the Californian San Andreas region. So we have had a good number of medium-hard shakes at both the top and the bottom of the San Andreas. The number of micro quakes has also grown much greater lately. Of course, the many millions of people in California living on top of this very restless earth are not supposed to be alarmed. My family has lived out there since the Gold Rush. We know these dangers and know that we must pay heed to them. Time to review earthquake preparations. Even the cautious geologists fearful of losing jobs are sounding a timid alarm.
A powerful earthquake capable of causing widespread destruction is 99 percent certain of hitting California within the next 30 years, scientists said Monday.
A new model devised to determine the probability of major earthquakes has found that the chances of a 6.7 magnitude earthquake not hitting California by 2038 was one percent, the US Geological Survey said.
The chances of a monster quake, measuring 7.5 or greater, were predicted at 46 percent over the same projected period, with densely populated southern California most likely to be affected.
The predictions were the result of a new system that combines information from seismology, earthquake geology, and precise measurements from the earth's surface, allowing the probabilities of a major earthquake to be forecast.
The group found that two of California's largest cities -- Los Angeles and San Francisco -- were more than 63 percent likely to face a 6.7 quake.
A 6.7 earthquake in Los Angeles in 1994 left 60 people dead and did an estimated 10 billion dollars damage, while a 6.9 quake in San Francisco in 1989 claimed the lives of 67 people.
Geologists say one of the biggest areas of concern in California is the southern section of the San Andreas fault in Riverside County, east of Los Angeles, which is described as being "10 months pregnant."
Geologists say the fault erupts with a large earthquake ever 150 years or so, but has not relieved tension in 300 years.
First off, there is a 100% chance of a 7+ earthquake. Hell's bells! These happen like clockwork! But the 9 mag deals: they are rare. They happen when a fault can't move for many years. There is a sector of the San Andreas that moved last when my great-great grandaddy crossed it. On horseback, of course. This newspaper article even mentions this sector! But don't show detailed maps, etc. Which is a shame. Many people and many water/transportation systems cross this sector and will see a probable sudden jump sideways of more than 45 feet in less than one second.
This map shows clearly how quakes have moved from a heavy dose of shaking at the important Juan de Fuca plate and now, at the bottom of California where the San Andreas plunges into the Gulf of California. Nearly all of last year, there were no quakes above 4 mag in this sector of the planet. Sumatra was very active. Now, Sumatra is very inactive. All the action is along the leading edge of the Australian part of the Indian/Australian plate, the part pushing the entire Pacific plate into the Juan de Fuca plate and the westward moving North American continent. This three way mighty clash is a big geological force creating earthquakes, tsunami and volcanos. Along with Japan, Sumatra and New Zealand, California is one of the most geologically active areas on earth.
When populations are fairly low and people live in palm frond huts, earthquakes are no great matter. Tsunamis are terrible and few structures can withstand them and they sweep away all humans in their path. And volcanos: nothing can stop a volcano. One can only run like hell. Truly, volcanos are tools of the gods as our ancestors believed.
Now, the section of the San Andreas the geologists mention in this short news story is not hard to find. Along one side of this fault rise the highest coastal mountains. In particular, this section has the highest of them all! These mountains aren't accidental. They are the result of violent earthquakes along here. My grandfather worked on and at the great observatories built on these mountains like Mt. Palomar and Mt. Wilson. I used to play there as a child. The mountains are so new, the sides are very, very steep. These aren't like the mountain I live on here in New York which is very rounded and fairly low, brought down by millions of years of erosion and glaciers. These mountains in California are very much teenagers and growing in spurts. Like teenagers, moody and prone to violence.
Let's look at the official 'probability maps from the geological survey: 24-Hour Aftershock Forecast Map
What Are Aftershocks, Foreshocks and Earthquake Clusters?
Aftershock Facts: In a cluster, the earthquake with the largest magnitude is called the main shock; anything before it is a foreshock and anything after it is an aftershock. A main shock will be redefined as a foreshock if a subsequent event has a larger magnitude. The rate of main shocks after foreshocks follows the same patterns as aftershocks after main shocks. Aftershock sequences follow predictable patterns as a group, although the individual earthquakes are random and unpredictable. This pattern tells us that aftershocks decay with increasing time, increasing distance, and increasing magnitude. It is this average pattern that this system uses to make real-time predictions about the probability of ground shaking.
Between Parkfield and just south of Los Angeles: this is the red hot danger sector. If you bookmark this web page, it lets you know what parts are the most active at this time. A good site to keep on the computer if living in California.
Click here for maps showing intensity of the 1857 quake along this section of the Sand Andreas that has not had any major quakes since then. This is possibly the most dangerous section of the San Andreas for it has not moved much since then and it is well over 150 years. The most serious mountain ranges on the coastal side of the Central Valley and Death Valley are along this fault line.
I took the official 'scenario' maps and linked them to the bigger map of California. If you click on the picture, it will enlarge and be much easier to read.
Below is an enlargement of the official government scenario maps for the sector of the San Andreas that is the least active this last 100+ years.
The nature of this beast is, if it is a 7 mag earthquake, it will be bad. If it is a 9 mag and that is quite possible, then it can cause landslides on the Los Angeles/Pasadena side of the mountains that rear up right over the Los Angeles basin. And if it is big enough, it can trigger other fault lines which can have secondary earthquakes at 7-8 mag levels. Like we saw very clearly in Sumatra with the Great Boxing Day Quake.
This map is from the USGS. I amended it to show the general location of the many water systems that carry water from the east to the biggest cities in California. All of these systems cross the San Andreas. If even half of them are severed, this will be a huge problem for LA. If LA takes damage in a major, 9 mag event along the eastern edge of the mountains, this can translate into a huge tragedy. This is why people in this sector should store a good supply of water in plastic containers that are stored on the ground. For example, I have a 250 gallon plastic storage tank with both a battery pump and a hand pump. But just gallon containers will be good. No one will want to drink from a toilet. But this is part of being in a major city that depends nearly 100% on water brought across some of the most active and dangerous fault lines on earth.