The HRSN data played an essential role in the discovery
of nonvolcanic tremors along the San Andreas Fault (SAF) below
Cholame, CA (Nadeau and Dolenc, 2005).
The location of the Cholame tremors occupies a critical location
between the smaller Parkfield ( M6) and much larger Ft. Tejon
( M8) rupture zones of the SAF. Because the time-varying nature
of tremor activity is believed to reflect time-varying deep
deformation and presumably episodes of accelerated stressing
of faults, and because an anomalous increase in the rate of Cholame tremor
activity preceded the 2004 Parkfield M6 by 21 days, we are
continuing to monitor the tremor activity observable by the HRSN
to look for anomalous rate changes that may signal an increased
likelihood for another large SAF event to the SE. Results of monitoring
effort are described further in the "Research" section of this
Map view (top, left), and across (bottom, left) and along SAF depth
sections (top and bottom, right) of double-difference
locations resulting from application of the similar event
pattern scanning and automated cataloging method using one event from
each of the SAFOD HI and SF target sequences as a reference.
The magnitudes of the 112 events ranged from 2.2 down to -1.4 Ml.
In the across fault sections at the right, inferred circular
dimensions of the event ruptures in the SAFOD zone are shown
as open circles assuming a 3MPa constant stress-drop model (top) and
an increasing stress-drop with decreasing magnitude model inferred
from recurrence interval information (Nadeau and Johnson, 1998).