Mexico was struck by two powerful earthquakes in less than two weeks, and the disasters have rattled the nerves of people in Southern California, too.
Take Two talked with Elizabeth Cochran, a seismologist with the United States Geological Survey in Pasadena, about whether those tremors could also occur here.
Is there any connection between these two earthquakes that hit Mexico City?
These two earthquakes are located quite far apart. So typically, this is outside of the range where we would consider yesterday's quake to be an aftershock of the earthquake on September 7th. However, it's right at the edge, so I think we could go either way in saying these are two related.
Could these trigger earthquakes here in California?
Well, actually we know that the magnitude 7.1 earthquake in Mexico yesterday did trigger a magnitude 3.6 earthquake in Coso, California.
Coso is located just up the 305 highway from Los Angeles going towards Mammoth. It’s what we call a geothermal area; this is an area that has a lot of heat and a lot of water moving around.
These types of areas tend to be very easy to trigger, so we often see remote earthquakes.
Anytime there’s an earthquake ... the waves actually do travel all around the world and cause very minimal levels of shaking. So what we saw during the [Mexican] earthquake is as those waves traveled through the Coso area an earthquake occurred there.
Should we be hyper-vigilant right now about earthquake threat?
There’s nothing in particular for us here in California that would indicate that we should be extra vigilant.
But, I think as always, we do need to be prepared for an earthquake here in Southern California.
Mexico has developed a pretty robust early warning system. Does yesterday's quake offer any lessons for officials here, who are also working on early warning?
Mexico developed an early warning system after the tragic 1985 earthquake which caused a huge amount of damage in Mexico City. They’ve now had an early warning system in place for about 20 years before yesterday's quake.
The earthquake was detected about 20 seconds before the shaking arrived in Mexico City. It's not clear if the residents of Mexico City actually received the alert through the siren system or on their cell phones.
We’re gonna have to look into that over the next couple days and weeks to see exactly how much warning they had.
My hope is that warning system was able to provide enough time to take protective action. What they recommend is that when people hear the sirens, they evacuate buildings.
That’s because they have a large number of vulnerable structures; we saw that yesterday as a large number of structures collapsed during the earthquake.
Here in California, it’s much less of concern. So the good thing about that is that with an early warning you only need five seconds or so to get under a desk or to protect yourself from objects falling in your office or home, rather than having to have tens of seconds to evacuate a building.