Very interesting earthquake sequence today, with vertical acceleration
records twice the horizontal for the M5.3 at 19:33 UTC. This event was
followed by two other events, M5.5 at 20:57 UTC and a M4.8 at 23:33 UTC.
The M4.8, being the closest to the WLA site, had the largest pore pressure
increase so far.
Pore pressure response is very interesting as well. First screenshot
(clickable for an expanded version) is all the pore pressure sensors
from shallow to deepest at the WLA site. Second screenshot is the
older re-instrumented USGS/NEES site (NP.5210) 80 meters from the
WLA site, with both 3-component acceleration and pore pressure
response shown on same plot.
This is the largest ground motion record we've recorded so far
at the NEES facility. No liquefaction, but another great example
of pore pressure ratcheting effect from multiple earthquakes, and
a good look at the details of the initiation phase of liquefaction.
These records demonstrate why continuous recording is so important
on these arrays. This high quality data is possible because of the
operations and maintenance funds supported through the National
Science Foundation's George E. Brown Jr., Network for Earthquake
Engineering Simulation program [Award numbers CMS-0217421, CMS-0402490,
and CMMI-0927178]. Real-time telemetry of this data back to UCSB and
Caltech is provided by the ANR/HPWREN system.