April 7, 2010

Magnitude 7.2, Baja California, April 4, 2010

By Hank Ratzesberger, Network for Earthquake Engineering Simulation - http://www.nees.org/

A major earthquake occurred at 3:40:40 PM on Easter Sunday, April 4, 2010. The magnitude 7.2 event occurred 83 km (39 miles) SSE of Calexico, California, in Baja Mexico and was 110 km (68 miles) from the Wildlife Refuge liquefaction field site. The site was fully operational, including real-time data streaming via the HPWREN wireless network. The UC Santa Barbara projects are one of the most intensive data generators on HPWREN.

The M7.2 event has provided a unique data set for the study of liquefaction. The peak ground acceleration recorded at the ground surface was just over 0.1g. Surface waves continued to shake the Imperial Valley for several minutes after the initial arrival of the earthquake.

The saturated sand layer at Wildlife did not liquefy during this event, yet an increase in the pressure of the groundwater was observed at all depths.

Ground and downhole acceleration was recorded at depths of 5.5, 8.5, 30 and 100 meters. The Wildlife and other sites operated by NEES@UCSB are among a handful of sites with dense instrumentation at strategic soil layer depths. Highly instrumented and thoroughly characterized, the sites provide a laboratory to test modeling of soil and seismic wave properties.

In addition to the permanent instrumentation, two temporary experiments were also deployed. The Advanced Site Monitoring experiment attempts to record permanent soil deformation to a depth of several meters, and the Mitigation Collapse experiment, part of a subproject dealing with nonlinear soil-structure interaction, is looking at rocking and uplift of a large-scale test structure.

Preliminary Data:

  • Garner Valley Station
  • Wildlife Refuge Station
  • 5210 Station

    External Links:

  • U.S. Geological Survey Quake Details
  • UCSB Press Release
  • Local News Article

    Main HPWREN web site (includes information for acknowledgments/disclaimers and feedback/contact)