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11,464 Earthquakes During Last 365 Days: Did You Feel Any Of Them?
This Caltrans photo shows damage to a state highway near Ridgecrest during California’s last large quake — the July 5, 2019 Ridgecrest-Trona earthquake that was 7.1 on the Richter scale.

I never travel into — or through — the Bay Area without making sure I have a full tank of gas.

The reason is simple. It’s because of what happened at 5:04 p.m. on Oct. 17, 1989 — the Loma Prieta earthquake.

My best friends at the time, Jack and Gail Vaughn, had seats almost behind home plate at Candlestick Park waiting for the third game of the World Series to start between the San Francisco Giants and the Oakland A’s when the 6.9 Richter Scale quake with an epicenter 10 miles northeast of Santa Cruz shook the Bay Area. Within 15 seconds, 63 people were killed, 3,757 injured, and $12.1 billion worth of damage in today’s dollars was done.

The fact the quake happened during the World Series that was an all-Bay Area affair meant commute traffic was lighter than normal. But given the double deck Nimitz Freeway in Oakland pancaked and crushed to death 42 people driving on the bottom level and a section of the upper level of the Bay Bridge collapsed, all bridges across the bay were shut down.

When the game was cancelled minutes later, their trip home to Pleasant Hill instead of being 55 minutes turned into a 10-hour ordeal. They had to drive around the South Bay through San Jose to get home. It was mostly on surface streets as freeways were at a complete standstill. They fortunately had adequate gas given power to most gas stations was knocked out.

The damage in Manteca — some 90 miles away — was limited to cracked patios and swimming pools. Also more than a few residents that had swimming pools reported water sloshing out.

I was 150 miles away at the time in Roseville at work at The Press-Tribune that was two blocks away from the Southern Pacific “hump yard” where freight trains are taken apart and individual boxcars and such are put into a system of tracks and switches at a slight grade to allow the boxcars to be formed into a new train.

Everyone in the building was pretty sure it was simply a boxcar that was rolling with a little bit too much momentum that created a loud thud and shock waves out that lasted for perhaps three seconds. About 20 seconds later, thanks to someone having a TV turned to the World Series, we realized it was a quake.

It wasn’t the first major quake I experienced. That was on Aug. 1, 1975 when a 6.4 magnitude quake centered near the base of Oroville Dam 48 miles from where I was at a Rotary meeting in a 1920s era building I was taking a photo at in Lincoln sent everyone running outside as the floor shook, light fixtures swayed, and a few dishes were shaken off tables.

Earthquakes are everywhere. The 1812 New Madrid quake estimated to be significantly more powerful at an estimated 8.2 compared to the paltry 6.9 Loma Prieta was so strong that it realigned segments of the Mississippi River and caused the river to flow backwards for several hours. Its biggest aftershock at 7.4 was much stronger than the 1989 Bay Area tremblor. The Great San Francisco Quake of 1906 was pegged at between 7.7 and 7.9 on the Richter scale.

There are quakes every hour in California. But unless they are over 3.0 you will not feel them. The smaller ones are all detected by sensors.

Around 9 p.m. on Jan. 27 there was a 2.1 quake six miles below the surface 40 miles west of Manteca in Danville according to the United States Geological Survey.

As of that hour in California there had been 14 quakes in the previous 24 hours, 174 quakes in the previous seven days, 849 quakes in the previous 30 days, and 11,464 quakes during the previous 365 days.

Those quakes that occur along the San Andreas Fault are helping move tectonic plates between 30 millimeters and 50 millimeters a year. At that pace, Los Angeles will be adjacent to San Francisco in 20 million years.

To see what land looks like along the fault nearest to Manteca, head south out of Manteca on Airport Way and you eventually cross the San Joaquin River.

At that point you are also crossing the closest earthquake fault to Manteca — the Vernalis Fault.

It starts near Dairy Road south of Highway 132 in Stanislaus County then runs north eventually paralleling Kasson Road, passing by the Deuel Vocational Institute and Banta before ending near the Old River northeast of Tracy.

According to the United States Geological Survey this is the inferred location. That’s because while it ranks as one of the state’s 500 most active faults — California has 15,700 earthquake faults — it hasn’t warranted much attention or mapping due to its low level of seismic activity.

Active when it comes to quakes and volcanoes is a relative concept. The Long Valley Caldera — identified as one of California’s most active volcanoes as well as its largest that is about 200 miles east of Manteca just south of Highway 120 on the way to Benton — last erupted 760,000 years ago. In comparison Mt. Lassen in the north state erupted in 1917.

Fault lines for the most part have substantially shorter time periods between significant events. The San Andreas Fault is in the high end of such a scale and the Vernalis Fault in the low end. That means in this area, we will likely feel shaking from a San Andreas quake 60 miles to the west more than once in our lifetime yet never feel any movement from the Vernalis Fault during the same time frame.

There are three other known faults nearby. Tracy-Stockton fault that runs under Stockton had significant shaking in 1881 and 1940. The epicenter of both was in Linden. The1940 event was 4.0 on the Richter scale. By comparison the 1989 Loma Prieta quake registered at 6.9 on the Richter scale.

The other nearby faults are the San Joaquin fault that runs along the base of the Coastal Ranges from east of Newman to east of Tracy. Then there is the Corral Hollow Fault a scientist discovered in 1991. Few faults are found actually in the Great Central Valley as the forces shaping California are found in the volcanic created Sierra and tectonic plates.

California is considered one of the most diverse geological areas in the world if not the most. A dozen major tectonic plates have given us a wealth of geological variation as well as extremes. The highest point in the United States — Mt. Whitney at 14,505 feet — is just 75 miles from the lowest point of Badwater found 282 feet below sea level in Death Valley.

The geographic extremity has also given California 12 microclimates, by far the most of any state. Because of that within California’s borders you will find the world largest living thing (a Sequoia tree composed of 52,508 square feet), the world’s tallest living thing (a redwood tree soaring 379.9 feet) and one of the world’s oldest living things (a bristlecone pine that’s 4,145 years old). You also will find the San Joaquin Valley that grows an eighth of the nation’s food.

The tectonic plates that keep moving against each other are the basic building block that created the state’s dozen microclimates.

Given what we are rewarded living on some real estate that is among the youngest on the planet is why I really don’t fret much about earthquakes.

Granted I may think a bit differently if I were attending Cal Bear football games where Memorial Stadium at Berkeley was built smack dab atop the very active Hayward Fault.