The City of Seismologists Gets Shook Up

Few American cities have as many resident seismologists and geologists as Pasadena. Fewer still come equipped with a world-class seismology laboratory and a field office of the U.S. Geological Survey.

Like everyone in Pasadena, Caltech administrators, faculty, students and USGS geologists were jolted by yesterday’s 4.4 earthquake centered just a few miles away from the Institute’s campus.

USGS seismologist Susan Hough said that she felt the earthquake while grabbing lunch at Browne Dining Hall on the Caltech campus. 

Allen Husker, research professor of geophysics at Caltech, reported feeling the quake on campus from his office in South Mudd.

“I was eating a salad, and I had to set it down and get under my desk,” Husker said. “It was a pretty nice jolt, though this earthquake was much shorter than the ones I felt when living in Mexico City.”

Husker and earthquake expert Lucy Jones, visiting associate in geophysics, along with other Caltech seismologists and members of the USGS provided information about the quake to the news media and public during a press conference hosted by the Caltech Seismological Laboratory within an hour of the temblor on Monday.

According to Jones, the earthquake occurred on the same fault system that produced the 1987 Whittier Narrows earthquake. Jones said this fault system is one of the most potentially dangerous in California as it runs underneath downtown Los Angeles. However, a magnitude 4.4 earthquake is unlikely to cause notable damage, she added.

Husker indicated that it is not possible to clarify the exact fault that caused the earthquake due to ambiguity in the delineation of faults, although evidence suggests that it was the Lower Elysian Park thrust fault or the Puente Hills fault.

Despite the relatively low magnitude of the quake, there was an influx of reports across the Los Angeles area to the USGS “Did You Feel It?” earthquake shake mapping tool following the event.

“The reason so many people felt shaking is because there were a lot of people on top of this earthquake,” said Jones at the press conference.

USGS seismologist Susan Hough said there were more than 20,000 reports made in the hours following the earthquake, and encourages anyone who felt the earthquake to report their experience.

Caltech staff seismologist Gabrielle Tepp said that as of 3:45 p.m., the Seismo Lab had recorded five aftershocks following the quake, with the two largest registering a magnitude 2.1. While there remains some possibility of a larger earthquake to come, the likelihood decreases over time.

“Any earthquake in California has a one in 20 chance of something bigger following,” said Hough. “But it would likely only be slightly larger than a 4.4 magnitude.”