Seismology Lab Director Explains Reno's Big Jolt

Dec 23, 2015

  

Map of last night's earthquakes.
Credit Nevada Seismology Lab website

  As many Renoites were falling asleep Tuesday night, a series of earthquakes sent strong jolts throughout the Truckee Meadows. Earthquakes aren’t new to the state, but the size of this one did get the attention of scientists at the Nevada Seismological Lab. To learn more, our reporter Julia Ritchey called up Graham Kent who directs the lab here at UNR.

Q: What did we feel Tuesday night?

Kent: “Well, you hopefully felt more than just one if you were awake. The largest was a magnitude 4.4, located about 3 miles north of Galena High School. It was a normal fault, which is interesting in terms of what that might mean. It was a very strong jolt. There were about five earthquakes above magnitude 3 in that little sequence there around 10:30 last night.”

You said it was a normal fault, what does that mean exactly?

Kent: “Yeah, we don’t tend to see those earthquakes very much in this area. We tend to see some of these smaller strike-slip faults light up. And the reason why it’s a little bit interesting is that the larger earthquake fault lines in this region are normal faults, including in the Reno Basin … so if we were to have a large earthquake, it would be on one of these normal fault structures. …Obviously, we had a middle-sized earthquake on one of those, so it brings a little extra attention.”

When’s the last time a temblor of this size was felt this widely?

Kent: “Last time was the Mogul event, which was in 2008 in the northwest part of town. …They ended up having about three magnitude 4 or above stretched out over a long period of time with a lot of little ones in between. …The largest one was just shy of magnitude 5 — that came later in the sequence. Then the only other one close to this was back in 2013 back up by Spanish Springs, and it was a little smaller than this.”  

What’s the day after an earthquake like at your lab?

Kent: “As you can imagine, it starts right away and keeps going. One of the things is to make sure that we pick all the earthquakes to understand smaller ones and where the sequence is and what it might mean. Also, it’s about going back and figuring out what didn’t work so great. One of the things is our website just got mauled and went down for an hour. …It’s another reason we need to put [the website] on the cloud to sustain these urban events where people hit it real hard.”

Could this be the start of a so-called swarm, where there’s a series of earthquakes?

Kent: “Well, that’s one of the things we always look for. We don’t know that till after the fact. But we do know a lot of earthquakes in Nevada tend to come in swarms. …We’re keeping our eyes peeled for that. A lot of the larger earthquakes historically in our region have started as swarms. On the other hand, not all swarms can become large earthquakes — so we’re always caught between a rock and a hard place. ...I think this a definite call that people drop, cover and hold on when they feel shaking. They can go to shakeout.org/Nevada to look how to prepare your space. …We always try to encourage resiliency in terms of what you can personally do.”