We conclude that forerunning activity was triggered as stress built up along the more active nearby San Andreas fault. This enabled us to identify a distinct nearby Lake Elsman fault zone in which precursors occurred in the 15 months prior to 1989. This was typically a 50 times increase in precision compared to those of routine locations in the area. This greater precision resulted from the use of so-called double-difference computations of the locations and origin times for many nearby earthquakes using digital waveforms from a large number of local seismograph stations. Here we pay particular attention to the detailed geometry of preceding seismic activity from 1984 to the 1989 mainshock using a catalog where hypocenters are located with respect to one another with precisions of 10s of meters or better. Relatively little work, however, has been devoted to forerunning activity. Aftershocks of the 1989 event have been described in detail. Hundreds of papers were published for the 1989 mainshock and its effects. The very long-period magnitudes, Mw, for the 19 earthquakes are 6.9 and 7.9. It ruptured a 40 km segment of the San Andreas fault zone in the geologically complex southern Santa Cruz mountains where a component of compressional contemporary deformation occurs in addition to the more typical strike-slip plate motion observed along much of the longer 1906 rupture zone farther northwest. It was the largest earthquake in the Bay area since the great shock of 1906.
#1990 california earth quake series#
Many remember it as the World Series earthquake. The Loma Prieta earthquake of Octokilled 63 people and caused billions of dollars of damage in the greater San Francisco Bay area of California even though it was located 40 to 60 km south of the city. Similar possible precursory activity very close to the San Andreas and other High-preci - sion locations readily available in real-time might be used to monitor
The occurrence of Lake Elsman earthquakes of magnitude 5.3 and 5.4 in 1988 andġ989. Not been the site of events of magnitude 5 and larger for many decades prior to Of the San Andre as Fault zone, the location of the 1989 mainshock, had The southern Santa Cruz mountains segment Increases just before the 1989 mainshock and a decrease in activity there after.
With little forerunning seismic activity in the region after 1906, la ter From the occurrence of the Lake Elsman shocks, weĭeduce that stress drop was only restored in the 15 months prior to the 1989 That zone experienced a relatively large stress decrease during the nearby greatĮarthquake of 1906. Of a prominent intermediate-term (yearly) precursor very close to theĬoming 1989 mainshock. That feature, which we call the LakeĮlsman fault zone, is identified as the site That separate zone broke in theġ5 months prior to the 1989 mainshock. Nearly the same orientation as the mainshock.
Magnitude 4.3 to 5.4 and smaller micro-earthquakes define a distinct zone of
We use precise locations of earthquakes to studyįorerunning seismic activity to the 1989 Loma Prieta earthquake of magnitudeĦ.9 to the south of San Francisco, California, USA.
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