No, the Mexico Earthquakes Won't Trigger Earthquakes in Pasadena

Local scientists dispel rumors, lament slow pace of earthquake early warning system

Published : Friday, September 22, 2017 | 5:56 AM

As a spate of major and minor earthquakes have recently wreaked havoc upon Mexico and throughout the Pacific “Ring of Fire,” the popular theory is that this has now increased the chances that Southern California will now get one of its own much sooner than later.

Not so, say prominent local geologists.

“The good news is earthquakes, large earthquakes in other locations far away, don’t have an impact on California,” says Doug Given, earthquake early warning coordinator for the U.S. Geological Survey.

“The bad news is that California is still earthquake country, and we have built up stresses here locally over the last 150 years or so that will ultimately lead to a big earthquake in Southern California, so the danger is still as great as it ever was. But it’s not increased by other events,” says Given, who added that people have the perception that earthquakes happen in clusters.

“Sometimes they do anyway in the process,” Given explained, and the media will often report them as such. But, says Given, there is often no actual connection.

And earthquake weather? “Earthquake weather is a fallacy,” he says, emphatically.

According to Ken Hudnut, science advisor for risk reduction at the US Geological Survey in Pasadena, the way that the recent earthquakes in Mexico are related is that both of those earthquakes were “extensional type.”

Hudnut explained, “It’s what we call normal faulting within the subducting slab, so there is a complex geometry to that slab. Those events happen far apart in space and not all that far apart in time, so they’re not a standard aftershock type of a relationship, but in the sense that they are both in the downgoing slab, it’s possible they are related in that way. Those two events may be related, but other ones elsewhere around the world, those may be only coincidental in terms of their time and occurrence.

As Hudnut explained further, “What happens is people start to see patterns, and once people’s attention is on earthquakes in general as right now with activity and the damage in Mexico, people tend to be more alert and paying more attention to smaller earthquakes that are happening worldwide, so when we have looked at the past, when people have thought there were patterns in these global earthquake occurrences, statistical analyses have shown that it hasn’t panned out to be anything supportable in any kind of statistical analysis.”

Asked whether or not an earthquake in Mexico can trigger a major quake in Southern California, Hudnut is reluctant to make that leap. A quake in Mexico would have to follow a pretty complicated road map to get to Pasadena, he says.

“We’re pretty far north,” says Hudnut, “You actually have to cross a major tectonic plate down there to get from where this activity is happening to where we are in California and that’s a very big step when you go across that plate boundary. To get from there to here you need to jump across what’s called the east pacific rise to get up here, and then up here, we have the Pacific plate heading northwest relative to the North American plate along the San Andreas Transform Boundary. So, to get to here from there you need to go across a boundary that probably does not support much in the way of stress changes, so we really wouldn’t expect to see that kind of triggering.”

In other words: that doesn’t happen.

Hudnut is also quite clear on the “earthquake weather” theory.

“There is no basis for any particular kind of weather pattern being called ‘earthquake weather.’ There is nothing to it at all, period,” he stresses. “There is no connection. The weather is happening above the earth’s surface, and the earthquakes are happening well below the earth’s surface, and there is no basis for any connection whatsoever.”

Meanwhile, California lags behind second and even third world countries in the development of a working earthquake warning system.

As Hudnut explains, the pace for its development and implementation is based on several factors.

‘It’s being developed in a prototype stage now, and we are doing pilot studies,” he says. “The situation here is that we have faults not only the san andreas fault which is at closest about 30 miles from LA. ‘We also have faults that are right underneath Los Angeles. The earthquakes in 1933, 1971 and 1994, all struck within the LA basin, and because of that close proximity, it’s difficult to develop an early warning system for those close-in cases, so what we are working on is a system that we believe will work with a low false alarm rate, but we don’t want to make it publicly available until it’s really ready for that so we are working on it still.

According to Hudnut, a warning system is also contingent on a lot of government cooperation, which has been slow in coming.

“We have had a lot of buy-in from the city of Los Angeles and other agencies,” he said, “but it really takes a concerted effort of both the state and federal governments, to put all the resources together that are needed. It’s not something that you can just do quickly and easily for not much cost.

Hudnut continued, “We are still in the process of converting what was a research network for observing earthquakes here in Southern California back in the early days here at Caltech. That network has been brought up to speed so that it can support rapid data handling, and that’s what you need to do earthquake early warning, but more sensors are needed, and even better, more perfected automation of our software. That’s where we are working hard on all these things concurrently, and so we appreciate the support that we have had so far, and we continue to need additional support in order to make this real so that people can have that earthquake early warning.”

And according to renowned and now retired former Caltech professor Lucy Jones, a local fixture with regard to Southern California earthquakes, there is another morbid reason why work on such a system is slow.

“It’s because we haven’t killed enough people in an earthquake yet.”

As Jones explains, “Every country that has an outreach cell system, lost at least 2000 people in an earthquake and that led them just to do the funding. We don’t have a lot of earthquakes in our capital. So the National level has often seen this as a ‘California only’ problem. That’s far from the case. Washington is a California problem.”

And when the big one does arrive, says Jones, “Ignore magnitude. We need to be talking about seismic intensity. It is that shaking that you’re receiving.”

“So the magnitude is totally terrifying,” she continued. “Intensity is telling you what shaking you’re getting. So people are just hearing intensity, not magnitude. So (we) can get out a warning system that says intensity 6 is coming. And people know what that means. Same if there’s a magnitude 6, that’s telling you how far away you are and what’s going to happen to you.

“When we do have a big San Andreas earthquake, imagine it ruptures at the fault. When it goes about 200 miles, that will be a 7.8, and the rupture will move close to Los Angeles, and that becomes a lot of damaging shaking here.

“And so we’re going to have this changing message about when or how strong it’s shaking, and when it’s going to be arriving,” says Jones. “People have to be ready for that. So that requires education about ideas like ‘a bigger earthquake lasts for a long time.’ And it’s coming from the epicenter, and some of it is coming at you from a different part of the world. And everything in the fault is shaking. We don’t know how big it is until it’s over.”

blog comments powered by Disqus