Seismicity and stress‐drop in the Eastern Transverse Ranges, southern California

Jones, Laura; Helmberger, Donald V.

doi:10.1029/96gl00012

Cited by 21 publications

(18 citation statements)

References 11 publications

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“…Most of the recorded aftershocks are in three off-fault clusters, suggesting static or dynamic triggering from the mainshock. The high stress drop in the mainshock suggests high stresses at depth, near the brittle ductile transition zone, consistent with previous studies (e.g., Jones and Helmberger 1996). The discrepancy between ML and Mw is further consistent with expectations for a high stress-drop event.…”

Section: Discussionsupporting

confidence: 81%

Preliminary Report on the 29 July 2008 Mw 5.4 Chino Hills, Eastern Los Angeles Basin, California, Earthquake Sequence

Hauksson

Felzer

Given

et al. 2008

Seismological Research Letters

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Section: Discussionsupporting

confidence: 81%

Preliminary Report on the 29 July 2008 Mw 5.4 Chino Hills, Eastern Los Angeles Basin, California, Earthquake Sequence

Hauksson

Felzer

Given

et al. 2008

Seismological Research Letters

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“…Due to the different modeling assumptions and the large scatter in the estimated stress drops, comparing the absolute values of Δσ in our result with those from the previous studies in the area (e.g., Jones and Helmberger, 1996;Shearer et al, 2006) is not that meaningful. Particularly, the results from most previous studies (e.g., Mori and Frankel, 1990; Figure 20.…”

Section: Discussionmentioning

confidence: 74%

Rupture Directivity Characteristics of the 2003 Big Bear Sequence

Tan¹,

Helmberger²

2010

Bulletin of the Seismological Society of America

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We have developed a forward modeling technique to retrieve rupture characteristics of small earthquakes (3 < M < 5), including rupture propagation direction, fault dimension, and rupture speed. The technique is based on an empirical Green's function (EGF) approach, where we use data from collocated smaller events as Green's functions to study the bigger events. We tend to choose smaller events with similar focal mechanisms for EGFs; however, we show that the events with different focal mechanisms can work equally well when corrected for radiation pattern effect. Compared to deconvolution, this forward modeling approach allows full use of both the shape and amplitude information produced by rupture propagation. Assuming a simple 1D source model, we parameterize the source time function of a target event as the convolution of two boxcars, featuring the rise time τ r and the rupture time τ c ; we solve for τ r and τ c in a grid search manner by minimizing the waveform misfit between the three-component data and the synthetics constructed from the EGFs. The rupture propagation direction, fault length, and rupture speed can then be estimated by fitting the observed azimuthal pattern of τ c from P and S waves. We apply the approach to the 12 largest events (M w ≥ 3:3) of the 2003 Big Bear sequence (excluding the mainshock) in southern California. Among them, seven events are found to exhibit robust rupture directivity. The fact that the ruptures of these events propagate in all directions reveals complicated fault geometry at depth. We compute the stress drop Δσ ∼ 2 π M 0 L 3 for each event using the resolved fault length. The results show large variations ranging from ∼1 to 90 Mpa, with no dependence on moment. However, Δσ appears inversely correlated with rupture speed V r ; in particular, events with larger Δσ tend to propagate at smaller V r , whereas events with smaller Δσ propagate faster.

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“…Following Cohn et al (1982) and Jones & Helmberger (1996) we estimate the stress drop (bars) to be Following Cohn et al (1982) and Jones & Helmberger (1996) we estimate the stress drop (bars) to be…”

Section: S E I S M I C M O M E N T a N D S T R E S S D Ro Pmentioning

confidence: 99%

The Afar Depression: interpretation of the 1960-2000 earthquakes

Hofstetter

Beyth

2003

Geophysical Journal International

102

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SUMMARY We studied the seismic activity of the Afar Depression (AD) and adjacent regions during the period 1960–2000. We define seven distinct seismogenic regions using geological, tectonic and seismological data. Based on the frequency–magnitude relationships we obtain b‐values of about 1 for the different regions. The pattern of the distribution of the location of epicentres fits with the known active fault zone in the AD and the axial volcanic ridges. The Bab el Mandab area and the Danakil‐Aysha'a blocks are less active. For 125 intermediate to strong earthquakes the seismic moment and source parameters were calculated. The results of the fault plane solutions for the Afar Depression indicate mainly strike‐slip and normal sense of movement originating from fault planes striking NW–SE. These results indicate a clockwise block rotation described previously as a bookshelf model in central AD. There are a few right‐lateral faults east of Massawa with E–W‐striking fault planes. At the southern Red Sea, north of the Danakil block, the mixed focal mechanisms, with axial plane striking NW–SE, comprise several reverse faulting, strike‐slip motion and normal faulting. Right‐lateral movement was also calculated for a cluster of seismic events between the Manda Hararo and Alyata volcanic ridges along NW–SE‐striking faults. Along the N–S‐striking faults in the escarpment, at the western Afar margins, there are two distinct clusters of epicentres. The strong earthquakes at the southern cluster exhibit normal or strike‐slip motions. The intermediate to small earthquakes in the northern cluster exhibit reverse and strike‐slip motions. Mainly normal faults were calculated along NE–SW‐striking faults of the Ethiopian East African Rift. Estimates of the seismic efficiency suggest that the maximal values are about 50 per cent or less, implying that most of the motion is taken aseismically.

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Seismicity and stress‐drop in the Eastern Transverse Ranges, southern California

Cited by 21 publications

References 11 publications

Preliminary Report on the 29 July 2008 Mw 5.4 Chino Hills, Eastern Los Angeles Basin, California, Earthquake Sequence

Preliminary Report on the 29 July 2008 Mw 5.4 Chino Hills, Eastern Los Angeles Basin, California, Earthquake Sequence

Rupture Directivity Characteristics of the 2003 Big Bear Sequence

The Afar Depression: interpretation of the 1960-2000 earthquakes

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