Preliminary isoseismal map for the Sierra Madre, California, earthquake of June 28, 1991 UTC

Stover, C.W.; Reagor, B.G.

doi:10.3133/ofr91388

Cited by 2 publications

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“…Both events were deep thrust earthquakes and both were costly to the residents of metropolitan Los Angeles. The felt area for the Sierra Madre event was approximately 59,000 km 2, considerably less that the 110,000 km 2 felt area for the Whittier Narrows earthquake [Stover and Reagor, 1991]. For comparison, the 1987 Whittier earthquake had a seismic moment of about 1.0 x 10 •5 dyn cm as estimated from strong motion data [Hartzell and Iida, 1990] and 1.1 to 1.4x10 •5 dyn cm based on teleseismic waveforms [Bent and Helmberger, 1989], roughly 4-5 times the moment of the Sierra Madre earthquake.…”

Section: And Conclusionmentioning

confidence: 96%

Strong motion and broadband teleseismic analysis of the 1991 Sierra Madre, California, earthquake

Wald¹

1992

J. Geophys. Res.

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Short period and broadband teleseismic waveform data and three‐component strong motion records were analyzed to obtain the source parameters of the 1991 Sierra Madre earthquake. Close‐in strong motion velocity records (analyzed from 5 s to 5 Hz) show two distinct pulses about 0.35 s apart, requiring some rupture complexity. The near‐field shear wave displacement pulse from this event has a relatively short duration (about 1 s) for the magnitude of the event, requiring a particularly high average stress drop. To further constrain the rupture process, the data were used in a finite fault source inversion to determine the temporal and spatial distribution of slip. We chose a fault plane orientation striking S 62°W and dipping 50° toward the northwest as required by the distribution of aftershocks, the first motion mechanism and the teleseismic bodywave point source inversion. In addition to the aftershock locations, depth constraints are provided by teleseismic short period and broadband recordings which require a centroid depth of 10–11 km. Our inverse modeling results indicate that both the teleseismic and strong motion data sets can be fit with a compact rupture area, about 12 km2, southwest and up‐dip from the hypocenter. The average slip is approximately 50 cm, and the maximum slip is 120 cm. The seismic moment obtained from either of the separate data sets or both sets combined is about 2.8 ± 0.3 × 1024 dyn cm and the potency is 0.01 km3. Using the area of significant slip estimated from the finite fault inversion, the resulting stress drop is on the order of 150–200 bars.

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Section: And Conclusionmentioning

confidence: 96%

Strong motion and broadband teleseismic analysis of the 1991 Sierra Madre, California, earthquake

Wald¹

1992

J. Geophys. Res.

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The 1991 Sierra Madre earthquake sequence in southern California: Seismological and tectonic analysis

Hauksson

1994

Bulletin of the Seismological Society of America

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The (ML 5.8) Sierra Madre earthquake of 28 June 1991 occurred at a depth of 12 km under the San Gabriel Mountains of the central Transverse Ranges. Since at least 1932 this region had been quiescent for M ≧ 3. The mainshock focal mechanism derived from first-motion polarities exhibited almost pure thrust faulting, with a rake of 82° on a plane striking N62°E and dipping 50° to the north. The event appears to have occurred on the Clamshell-Sawpit fault, a splay of the Sierra Madre fault zone. The aftershock sequence following the mainshock occurred at a depth of 9 to 14 km and was deficient in small earthquakes, having a b value of 0.6. Twenty nine single-event focal mechanisms were determined for aftershocks of M > 1.5. The 4-km-long segment of the Clamshell-Sawpit fault that may have ruptured in the mainshock is outlined by several thrust focal mechanisms with an east-northeast-striking fault plane dipping to the north. To the west, several thrust aftershocks with east-striking nodal planes suggest some complexity in the aftershock faulting, such as a curved rupture surface. In addition, several strike-slip and normal faulting events occurred along the edges of the mainshock fault plane, indicating secondary tear faulting. The tectonic stress field driving the coexisting left-lateral strike-slip and thrust faults in the northern Los Angeles basin is north-south horizontal compression with vertical intermediate or minimum principal stress axis.

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Preliminary isoseismal map for the Sierra Madre, California, earthquake of June 28, 1991 UTC

Cited by 2 publications

References 0 publications

Strong motion and broadband teleseismic analysis of the 1991 Sierra Madre, California, earthquake

Strong motion and broadband teleseismic analysis of the 1991 Sierra Madre, California, earthquake

The 1991 Sierra Madre earthquake sequence in southern California: Seismological and tectonic analysis

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