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 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.
U.S. Geological Survey Quake Details