Topic
Foreshock
About: Foreshock is a research topic. Over the lifetime, 2877 publications have been published within this topic receiving 76246 citations.
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Papers
TL;DR: In this article, an initial moment tensor is derived using one of the variations of the method described in detail by Gilbert and Dziewonski (1975), where perturbations to the elements of the moments are found simultaneously with changes in the hypocentral parameters.
Abstract: It is possible to use the waveform data not only to derive the source mechanism of an earthquake but also to establish the hypocentral coordinates of the ‘best point source’ (the centroid of the stress glut density) at a given frequency. Thus two classical problems of seismology are combined into a single procedure. Given an estimate of the origin time, epicentral coordinates and depth, an initial moment tensor is derived using one of the variations of the method described in detail by Gilbert and Dziewonski (1975). This set of parameters represents the starting values for an iterative procedure in which perturbations to the elements of the moment tensor are found simultaneously with changes in the hypocentral parameters. In general, the method is stable, and convergence rapid. Although the approach is a general one, we present it here in the context of the analysis of long-period body wave data recorded by the instruments of the SRO and ASRO digital network. It appears that the upper magnitude limit of earthquakes that can be processed using this particular approach is between 7.5 and 8.0; the lower limit is, at this time, approximately 5.5, but it could be extended by broadening the passband of the analysis to include energy with periods shorter that 45 s. As there are hundreds of earthquakes each year with magnitudes exceeding 5.5, the seismic source mechanism can now be studied in detail not only for major events but also, for example, for aftershock series. We have investigated the foreshock and several aftershocks of the Sumba earthquake of August 19, 1977; the results show temporal variation of the stress regime in the fault area of the main shock. An area some 150 km to the northwest of the epicenter of the main event became seismically active 49 days later. The sense of the strike-slip mechanism of these events is consistent with the relaxation of the compressive stress in the plate north of the Java trench. Another geophysically interesting result of our analysis is that for 5 out of 11 earthquakes of intermediate and great depth the intermediate principal value of the moment tensor is significant, while for the remaining 6 it is essentially zero, which means that their mechanisms are consistent with a simple double-couple representation. There is clear distinction between these two groups of earthquakes.
3,081 citations
TL;DR: In this paper, the second-order moment (cross-correlation function) of earthquakes in the U.S. Geological Survey central California catalog between 1969 and 1982 was calculated with respect to a magnitude threshold M ≥ 4.0 over interevent distances up to 80 km.
Abstract: The second-order moment (cross-correlation function) of earthquakes in the U.S. Geological Survey central California catalog between 1969 and 1982 was calculated with respect to a magnitude threshold M ≥ 4.0 over interevent distances up to 80 km and interevent times up to 320 days. The statistical procedure results in a representation of the spatial-temporal structure of the catalog associated with M ≥ 4.0 earthquakes and is capable of revealing patterns too weak to be detected in the space-time distribution of seismicity for individual earthquake sequences. A method is introduced for identifying aftershocks based on a physical two-parameter model of the earthquake interaction process. The results show that the aftershock process dominates the second-order moment and may even obscure the statistical expression of a precursory process. A concentration of foreshocks within 15 km and 3 days of M ≥ 4.0 main shocks exhibits an apparent migration toward the main shock loci with velocity 2.6–5.3 km/d. This concentration may be related to an observed tendency for M ≥ 4.0 events to cluster (auto-correlate) over this interevent range. With the identified aftershocks removed, the residual catalog is Poissonion in space and time. When two M ≥ 4.0 earthquakes occur within 80 km and 40 days of each other, aftershock productivity appears to be relatively enhanced in the earlier sequence. This suggests that aftershock populations are not solely dependent on their main shocks and that unusually productive aftershock sequences may be predictors of future moderate earthquakes.
1,166 citations
TL;DR: In this paper, the authors used the aftershocks associated with a large earthquake as Green's functions to model the earthquake strong ground motion, and used the effects of the true earth structure are included in the modeling process.
Abstract: A method is presented for modeling earthquake strong ground motion, which uses the aftershocks associated with a large earthquake as Green's functions. A major earthquake, with a large rupture surface, is modeled by a collection of point sources distributed over the fault plane. The response of each point source is approximated by the ground motion of the closest associated aftershock. By using the aftershock responses, the effects of the true earth structure are included in the modeling process. This method is used to model the El Centro displacement record for the 1940 Imperial Valley earthquake.
875 citations
TL;DR: In this paper, the authors used static Coulomb stress changes associated with earthquake slip to explain aftershock distributions, earthquake sequences, and the quiescence of broad, normally active regions following large earthquakes.
Abstract: ▪ Abstract Earthquake triggering is the process by which stress changes associated with an earthquake can induce or retard seismic activity in the surrounding region or trigger other earthquakes at great distances. Calculations of static Coulomb stress changes associated with earthquake slip have proven to be a powerful tool in explaining many seismic observations, including aftershock distributions, earthquake sequences, and the quiescence of broad, normally active regions following large earthquakes. Delayed earthquake triggering, which can range from seconds to decades, can be explained by a variety of time-dependent stress transfer mechanisms, such as viscous relaxation, poroelastic rebound, or afterslip, or by reductions in fault friction, such as predicted by rate and state constitutive relations. Rapid remote triggering of earthquakes at great distances (from several fault lengths to 1000s of km) is best explained by the passage of transient (dynamic) seismic waves, which either immediately induce ...
802 citations
TL;DR: The time history of quasi-static slip along the plate interface, based on small repeating earthquakes that were part of the migrating seismicity, suggests that two sequences involved slow-slip transients propagating toward the initial rupture point.
Abstract: Many large earthquakes are preceded by one or more foreshocks, but it is unclear how these foreshocks relate to the nucleation process of the mainshock. On the basis of an earthquake catalog created using a waveform correlation technique, we identified two distinct sequences of foreshocks migrating at rates of 2 to 10 kilometers per day along the trench axis toward the epicenter of the 2011 moment magnitude (M(w)) 9.0 Tohoku-Oki earthquake in Japan. The time history of quasi-static slip along the plate interface, based on small repeating earthquakes that were part of the migrating seismicity, suggests that two sequences involved slow-slip transients propagating toward the initial rupture point. The second sequence, which involved large slip rates, may have caused substantial stress loading, prompting the unstable dynamic rupture of the mainshock.
779 citations
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Performance Metrics
| Year | Papers |
|---|---|
| 2025 | 64 |
| 2024 | 66 |
| 2023 | 185 |
| 2022 | 195 |
| 2021 | 94 |
| 2020 | 88 |