Tuesday, June 4, 2013 • Lassen County is earthquake country

Publisher’s note: This story originally appeared in the Tuesday, June 4, 2013, edition of the Lassen County Times.

It might just appear to be a bunch of damp dirt and a pile of fallen rocks to most of us, but Chester geologist Charles Watson paid a special visit to the shore of Lake Almanor just to get a firsthand look at the effects of the recent 5.7 magnitude earthquake.

The recent 5.7 magnitude earthquake may have startled some Northeastern California residents, including those in Lassen County, but we shouldn’t be all that surprised. The reality is our region, like the rest of California, is rightly called earthquake country.

Chester geologist Charles Watson, who prepares the weekly earthquake report for the Feather Publishing newspapers, said there is no way to predict where or when an earthquake might hit. But he said once an earthquake is recorded on a fault, another one could strike any time.

Believe it or not, the initial wave of an earthquake can force a rock up into the air. When it comes back down, the Earth beneath it may have moved and the rock will not return to the same place. Watson suspects the damp area near this rock along the Lake Almanor shore illustrates this movement.

Consider this: research near Honey Lake has revealed three and possibly four earthquakes with a magnitude of 7.0 or greater have rattled the area in the last 7,000 years on that fault alone, and Watson said there are dozens and dozens of faults in the region with that capability.

“We live in earthquake country,” Watson said. “It will happen at some point in time. (The recent quake) was a prime example of that. Earthquakes tend to happen at their own time and pace.”

In fact, geologist Mike Parker, a recent master’s graduate from Chico State University, said some geologists at a recent conference he attended expect earthquake activity may increase on the faults on the eastern side of the Sierra in the future.

Here’s another rock along the Lake Almanor shore that may have been displaced by the recent earthquake.

Watson said the recent earthquake was a tectonic event caused by the movement of the Earth’s plates that happens to be near a volcanic center. Contrary to some speculation by some media outlets, the temblor had nothing to do with volcanic Lassen Peak, and Watson said he and Parker planned a visit to the hot springs and creeks near the national park to test the water and look for any changes the earthquake may have caused to the magma chamber underneath the mountain.

According to Watson, a tectonic earthquake is similar to pulling a rubber mat across the floor. At first the mat doesn’t move, but once enough energy is applied, the mat jumps forward all of sudden. In this case it appears one of three faults about half a mile above the vista point near Canyon Dam — scientists have not decided which one yet — slipped.

Most of us might whiz by this rockfall with barely a second thought, but Chester geologist Charles Watson is fascinated by such events. He joked when a rock this size falls it could have caused an earthquake all by itself.

According to Watson, the quake occurred in the Mohawk Valley/Almanor fault zone, and that fault runs from Sierraville down to Lake Tahoe.

“It’s the western margin of what’s called the Walker Lane Shear Zone,” Watson said, “and that extends all the way down to Las Vegas and forms a boundary in the North American crust which is very prominent, and it’s been going on for millions of years. This earthquake was at the northern margin of all that where it meets up with Mount Lassen.”

Lassen Peak is about 20 miles north of the quake’s epicenter.

“The interesting thing is the quake occurred on the north side,” Watson said. “They usually occur on the south side. What’s going to be really interesting when we look at all the scientific data is whether this is a strike-flip earthquake like the San Andreas moving back and forth or is this like a Japan earthquake where it’s up and down — a thrust fault earthquake.”

He said an earthquake occurs when the rock fractures due to the strain of the plates trying to move. The rocks break, and the crack is a fault. After the rocks move, “they try to find a comfortable place to settle down and relax,” Watson said.

Generally there’s a first shock followed by a series of aftershocks, Watson said, but no one knows if the first quake is really a foreshock to a larger earthquake.

“It could be a month, it could be year, you never know if it could be a part of some larger event,” Watson said. “As you can see from the damage here, a much larger earthquake could cause some serious problems up here.

Even though the area is remote and sparsely populated, Watson said a large quake could still result in the loss of life.

Be prepared
Watson said, “Be aware you live in earthquake country. Be prepared.”

While duck, cover, hold is the California model for earthquake safety, Watson said he always adds think to the beginning of that list.

“Your first motion and movement can save your life,” Watson said.

He suggests residents always have emergency supplies and necessary medical supplies such as prescriptions on hand

In a rural area, Watson said it’s best to move outside in a large earthquake, but in a city, you’re better off to stay inside because of all the dangers posed by falling objects.

If you do elect to stay inside during a large earthquake, it’s best to stand in a doorway or get under a table.

Propane tanks will need to be shut off if the lines rupture, and large appliances such as refrigerators can move across the floor.

Make sure you don’t stand in front of a large picture window during a quake because the glass might shatter.

And be careful around shorelines because the water level may surge. Watson said the water level rose two feet at Lake Almanor during the recent quake.

“Our pets and the elderly are things we forget about but should remember,” Watson said. “We should be more of a community. Earthquakes and tornadoes tend to bring people together.”