Magnitude 4.4 Earthquake Rattles Caltech Campus and Greater Los Angeles Area

A magnitude 4.4 earthquake shook Caltech’s campus around 12:20 p.m. on Monday, August 12, and was felt across the greater Los Angeles area.

The earthquake’s epicenter was pinpointed near the border of South Pasadena and the Highland Park neighborhood of Los Angeles, roughly 5 miles from Caltech’s campus in Pasadena.

Caltech staff, students, and community members reported brief but strong shaking across campus, and the Institute delivered an email alert via the emergency notification system immediately after the earthquake. Caltech Facilities assessed campus building operations and services in the aftermath of the quake and there were no reported injuries or sustained interruptions to systems and facilities.

Allen Husker, research professor of geophysics; and Lucy Jones, visiting associate in geophysics; along with other Caltech seismologists and members of the U.S. Geological Survey (USGS), provided information about the quake to the news media and public during a press conference hosted by the Caltech Seismological Laboratory. 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.”

Hough said that she felt the earthquake while grabbing lunch at Browne Dining Hall on campus. Husker also 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.”