Researchers Discuss Baja California's "Easter Earthquake"

As a 7.2-magnitude earthquake rattled Baja California on April 4, 2010, scientists at Scripps Institution of Oceanography at UC San Diego were tracking the temblor along the U.S.-Mexico border using data from a network of seismic monitoring tools on the ground and in space. Scripps research teams will present preliminary research findings from ongoing studies of the so-called "Easter Sunday" earthquake during several presentations at the 2010 American Geophysical Union (AGU) Fall Meeting in San Francisco. Scripps Research Geodesist Yehuda Bock and colleagues at a GPS station in California's Cleveland National Forest.
Photo: Marc Tule Scripps Research Geodesist Yehuda Bock and colleagues at a GPS station in California's Cleveland National Forest. Photo: Marc Tule During several talks, Scripps research geodesist and 2010 AGU Fellow Yehuda Bock and colleagues will discuss data collected from the California Real-Time Network, a prototype early warning system that uses GPS satellites to detect the surface deformation triggered by large earthquakes. (G11C-07 · Monday, Dec 13, 9:30 a.m. · 2003 Moscone West and T51E-05 · Friday, Dec. 17, 9:00 a.m. · 2011 Moscone West) Within a day of the quake, Scripps geophysicists David Sandwell and Yuri Fialko headed to the U.S.-Mexico border city of Calexico on a rapid response research mission to deploy several GPS instruments near the rupture site to put together a picture of the ground movements. "Most of the deformation occurs in the first day or two after the earthquake, so it was important to get out there soon after the event," said Sandwell, who used GPS and satellite image data to capture the post-seismic deformation at the rupture site. Fialko, Sandwell and Scripps graduate student Meng Wei will discuss a slip model produced from surface deformation data to show how the fault moved at depth. Using satellite images, the team created a detailed map of surface motion that revealed more than 10 faults that moved during or soon after the quake, including the San Andreas Fault. The rupture produced both horizontal and vertical motion, which contributed to the complex pattern of seismic waves observed. (T53B-2125 · Friday, Dec. 17, 1:40 - 6:00 p.m. · Poster Hall Moscone South and T53B-2134 · Friday, Dec. 17, 1:40 - 6:00 p.m. · Poster Hall Moscone South) An interferogram derived from satellite data clearly shows the ground deformation and liquefaction cause by the An interferogram derived from satellite data clearly shows the ground deformation and liquefaction cause by the "Easter" earthquake A radar interferometry picture produced from satellite images by Sandwell's team also revealed the boundaries of a 20-kilometer-wide and 60-kilometer-long liquefaction zone. The agricultural area southwest of the ruptured fault produced sand volcanoes where the earthquake-induced stress liquefied the soil. "These findings have important implications to seismic hazard assessment in Southern California," said Wei. Scripps scientists Catherine de Groot-Hedlin and Kris Walker will present an analysis of infrasound array data recorded in Southern California, which indicates that the surface shaking generated low-frequency sound waves that reached nearly 200 kilometers (124 miles) north and west of the epicenter. The research team used data recorded by an array near San Diego to model the surface shaking in the vicinity of the rupture and compared their results with U.S. Geological Survey ShakeMaps. (T53B-2119 · Friday, Dec. 17, 1:40 - 6:00 p.m. · Poster Hall Moscone South) Prior to this temblor, the largest earthquake to shake Southern California was the 7.3-magnitude Landers earthquake, which occurred in the Mojave Desert in 1992. The 2010 Easter quake's epicenter was approximately 51 kilometers (32 miles) southeast of Mexicali in Baja California, Mexico and was felt as far away as Las Vegas. # # # RELATED PRESENTATIONS: G11C-07 · Monday, Dec 13, 9:30 a.m. · 2003 Moscone West "RAPID MODELING OF AND RESPONSE TO LARGE EARTHQUAKES USING REAL-TIME GPS NETWORKS" (INVITED) T51E-05 · Friday, Dec. 17, 9:00 a.m. · 2011 Moscone West "OBSERVATIONS AND MODELING OF THE MW 7.2 2010 EL MAYOR-CUCAPAH EARTHQUAKE WITH REAL-TIME HIGH-RATE GPS AND ACCELEROMETER DATA: IMPLICATIONS FOR EARTHQUAKE EARLY WARNING AND RAPID RESPONSE" (INVITED) S52A-03 · Fri, Dec 17, 10:50 a.m. · 2009 Moscone West "COMBINING HIGH RATE GPS AND STRONG MOTION DATA: A KALMAN FILTER FORMULATION FOR REAL-TIME DISPLACEMENT WAVEFORMS" T53B-2119 · Friday, Dec. 17, 1:40 - 6:00 p.m. · Poster Hall Moscone South "INFRASONIC OBSERVATIONS OF GROUND SHAKING ALONG THE 2010 MW 7.2 EL MAYOR RUPTURE" T53B-2125 · Friday, Dec. 17 1:40 - 6:00 p.m. · Poster Hall Moscone South "STATIC RUPTURE MODEL OF THE 2010 M7.2 EL MAYOR-CUCAPAH EARTHQUAKE FROM ALOS, ENVISAT, SPOT AND GPS DATA" T53B-2134 · Friday, Dec. 17, 1:40 - 6:00 p.m. · Poster Hall Moscone South "SLIP ON FAULTS IN THE IMPERIAL VALLEY TRIGGERED BY THE 4 APRIL 2010 MW 7.2 EL MAJOR EARTHQUAKE AS REVEALED BY INSAR"