A systematic test of the hypothesis that the <i>b</i> value varies with depth in California

Gerstenberger, Matt; Wiemer, Stefan; Giardini, Domenico

doi:10.1029/2000gl012026

Cited by 111 publications

(89 citation statements)

References 17 publications

(13 reference statements)

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“…The global upward migration of seismicity is driven by the shallow shallow seismicity pattern. trano, 2003) and reported for genuine earthquakes (e.g., Mori and Abercombie, 1997;Gerstenberger et al, 2001, Sue et al, 2002. Another alternative is that the b-value variations are the result of shallow earthquakes moving toward the surface: the closer an event to the Earth's surface, the less the probability that a large earthquake would occur at such a depth; hence the seismicity near the surface is depleted of large shocks.…”

Section: Discussionmentioning

confidence: 99%

A Long-Lasting Relaxation of Seismicity at Aswan Reservoir, Egypt, 1982-2001

Mekkawi¹

2004

Bulletin of the Seismological Society of America

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The Aswan reservoir seismicity is accepted as an example of reservoirinduced seismicity with the M 5.4 event of 1981, which occurred 15 years after the reservoir impoundment started. During the 1982-2001 period, the Aswan seismicity separates into shallow and deep seismic zones, between 0 and 15 and 15 and 30 km, respectively. These two seismic zones behave differently over time, as indicated by the seismicity rate, depth migration, b-value, and spatial clustering. For the deep events, the rate decreases with time, the depth remains at a constant or increasing depth, and the b-value is lower than for the shallow events, which migrate toward the surface with a close to constant seismicity rate. Of all the previous parameters, only the seismicity rate correlates with seasonal variations of the lake level. This is positive evidence for the Aswan reservoir seismicity to be reservoir triggered in the 1982-2001 period. Clustering over time and space expresses that numerous aftershock sequences are activated, that is, a minimum of 35% of the seismicity, similarly to tectonic seismicity. The observed decrease of the b-value with depth is also a property suggested for natural events. Our results suggest that the Aswan seismicity emerges both from the water-level loading and the interplay between induced earthquakes themselves through numerous standard aftershock sequences. This latter process induces stochastic fluctuations in the seismicity patterns that inhibit a recovery of a simple seismic response to water-level changes. Even though aftershock sequences dominate the temporal fluctuations of seismicity, this does not negate the importance of influence of the reservoir in sustaining this unusual long-lasting seismic episode. During the 1982-2001 period, the Aswan seismicity appears as a powerlaw relaxation response to the 1981 M 5.4 shock, this response being decorated by long-term (larger than 100 days) water-level changes.

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Section: Discussionmentioning

confidence: 99%

A Long-Lasting Relaxation of Seismicity at Aswan Reservoir, Egypt, 1982-2001

Mekkawi¹

2004

Bulletin of the Seismological Society of America

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“…In laboratory experiments (e.g., MOGI, 1962;SCHOLZ, 1968;MEREDITH et al, 1990;AMITRANO, 2003) and in mines (URBANCIC et al, 1992), they observe correlations between the b-values and stress. In the case of natural earthquakes, it has also been observed that the b-values change with depth, possibly owing to increasing stress with depth (e.g., MORI and ABERCROMBIE, 1997;GERSTENBERGER et al, 2001;SUE et al, 2002).…”

Section: Introductionmentioning

confidence: 99%

Tidal Stress/Strain and the b-values of Acoustic Emissions at the Underground Research Laboratory, Canada

Iwata

Young

2005

Pure appl. geophys.

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The correlation between the b-values of acoustic emissions (AEs) and the phase of the moon was investigated at the Underground Research Laboratory (URL) in Canada. The same data as those used in IWATA (2002) were examined, which showed that the occurrence of AEs is correlated with the phase of the moon. It was expected, therefore, that the b-value of the AEs would also be sensitive to tidal stress/ strain fluctuations. We investigated the variation of the b-values as a function of the phase of the moon. Results show that b-values immediately following the times of full/new moon are higher than those at other times. Using AIC (Akaike Information Criterion) and random (Monte Carlo) simulations, it was confirmed that this feature is statistically significant. We also investigated whether or not there was a change in the b-values immediately before the times of full/new moon, but no statistically significant change was observed. The results suggest that the effect of stress/strain fluctuations on AE occurrences at the URL is asymmetric to the times of full/new moon.

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“…Strong spatial variations of the earthquake size distribution expressed in terms of the b-value, on scales of 1-50 km, have also been determined in different tectonic regimes, ranging from small scales, such as volcanic systems (Wiemer and McNutt, 1997;Wiemer et al, 1998), to regional scales (e.g., Ogata et al, 1991;, Gerstenberger et al, 2001a. Stress is also a factor involved in perturbing the b-value (Urbancic et al, 1992;Wyss, 1973;Lahaie and Grasso, 1999;Wiemer and Wyss, 2000).…”

Section: Introductionmentioning

confidence: 99%

Properties of the Aftershock Sequence of the 1999 Mw 7.1 Hector Mine Earthquake: Implications for Aftershock Hazard

Wiemer¹,

Gerstenberger²,

Hauksson³

2002

Bulletin of the Seismological Society of America

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We investigate the spatial and temporal seismicity parameters and the related probabilistic aftershock hazard for the aftershock sequence of the 1999 M w 7.1 Hector Mine mainshock and compare it with the neighboring 1992 M w 7.3 Landers sequence. Using a catalog of 11,000 earthquakes, we determine the earthquake size distribution (b-value), the aftershock decay rate (p-value), and the seismic activity rate (a-value). The b-values are high (b Ͼ 1.2) within the rupture area, significantly lower (b Ϸ 0.7) north of the rupture area, and increase with time since the mainshock. Probabilistic aftershock hazard maps, computed automatically as early as 4 days after the mainshock, identified the northernmost part of the sequence as the highest-hazard region. These maps show a good agreement between the forecasts and the recorded large aftershocks. Based on the asymmetrical b-value and hazard patterns for both the Hector Mine and Landers sequences, we hypothesize that the mainshock rupture directivity and slip distribution influence aftershock hazard. Current static or dynamic stress triggering models cannot resolve this spatial and temporal evolution of the hazard. Stress tensor inversions of 1400 relocated first-motion focal mechanisms show predominantly a strike-slip stress state with a SW-NE trend of the greatest principal stress. The heterogeneity of the stress field is unusually high near the Hector Mine and Landers mainshock ruptures, particularly near patches of large slip.

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A systematic test of the hypothesis that the b value varies with depth in California

Cited by 111 publications

References 17 publications

A Long-Lasting Relaxation of Seismicity at Aswan Reservoir, Egypt, 1982-2001

A Long-Lasting Relaxation of Seismicity at Aswan Reservoir, Egypt, 1982-2001

Tidal Stress/Strain and the b-values of Acoustic Emissions at the Underground Research Laboratory, Canada

Properties of the Aftershock Sequence of the 1999 Mw 7.1 Hector Mine Earthquake: Implications for Aftershock Hazard

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