Stress Dissipation in the North-West Himalaya: What We Learnt from Post-seismic Stress Changes
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[EMBARGOED UNTIL 5/1/2023] This work focuses on characterizing spatiotemporal patterns of earthquakes, their possible causes, and their implications for seismic hazard assessment. I studied both local and global earthquakes in the view of complex fault systems. Specifically, I studied the background seismicity and long-lived aftershock activities in intraplate North China and the Central and Eastern United State (CEUS), and characterized the correlation between strain rate and seismicity and evaluated the prediction power of strain rate in different tectonic settings. I found that periodic or quasiperiodic earthquake recurrence on individual faults, as predicted by the elastic rebound model, is not common in nature. Instead, most earthquake sequences are complex and variable, and often show clusters of events separated by long but irregular intervals of quiescence. The common earthquake clustering may be caused by earthquake-induced viscoelastic relaxation and fault interaction. Most earthquake sequences are burstier than the Poisson model, implying a higher probability of repeating events soon after a large earthquake. Possible long-lived aftershocks are found in intraplate North China and the CEUS. Background seismicity in intraplate regions may vary with time, highlighting the complexity of intraplate seismicity. Mistakenly identifying long-lived aftershocks as background earthquakes may overestimate seismic hazard in intraplate regions. The correlation between strain rate and seismicity varies between different tectonic settings and is time-dependent. Good strain rate-seismicity correlations are found in plate boundary regions and during seismically active periods, while no correlations are found in stable continents and during inactive periods. All these variations need to be considered in hazard assessment.
Remotely triggered earthquakes
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Seismotectonics
Seismic risk
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Seismogenic Index of a Reservoir Location Estimated from Tectonic Seismicity and Crustal Deformation
We address the question whether tectonic seismic activity within an area where a fluid injection is planned can be used to evaluate its seismotectonic state. For this purpose, we expand and reformulate the theoretical framework which essentially applies to describe the occurrence of fluid-induced seismicity to the case of tectonic seismicity. Based on this model, we introduce the tectonic seismogenic index which can be determined prior to an injection if the tectonic seismicity rate and the crustal deformation rate are known in the reservoir region. We apply the derived formalism to reservoir locations where the seismogenic index for fluid-induced seismicity had already been obtained. Thus, we can examine whether the two differently defined seismogenic indices are comparable for an injection location. Our results show that the tectonic seismogenic index can be used as a proxy for the seismogenic index of fluid-induced seismicity. Thus, we conclude that our formalism can contribute to avoid the occurrence of large-magnitude fluid-induced earthquakes by properly selecting and developing reservoir locations.
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Abstract We investigate probabilistic seismic hazard analysis (PSHA) in low-seismicity regions in which epistemic uncertainties are largely due to the sparsity of data, with a focus on Finland, northern Europe. We investigate the sensitivity of site-specific PSHA outcomes to different choices of basic input parameters, starting from preexisting PSHA models of the nuclear licensees in the country, without producing a final hazard curve. The outcome shows that the parameters and models needed to estimate future seismicity rates from actual observations, in particular the b value, seismicity rates, and the largest possible magnitude, M max , as well as the median ground-motion prediction equation, play significant roles. The sensitivity also depends on the spectral frequency; for example, the effect of M max is significant especially for a low-frequency hazard at annual frequency of exceedance 10 −5 but more moderate for peak ground acceleration. The delineation of seismic source zones (SSZs) remains ambiguous in regions of low seismicity. This, combined with the dominance of the host SSZ and its seismicity parameters, may have a substantial impact on the outcome. Our results are quantitatively applicable to Finland, but may also be of relevance to other low-seismicity regions in Europe and elsewhere. For future work we recommend the exploration of PSHA sensitivity with focus on the host SSZ with its immediate vicinity and the b value around the site of interest.
Spectral acceleration
Maximum magnitude
Microseism
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Abstract The Sumatra subduction zones have been known to produce large destructive earthquakes and tsunami, such as the 26 December 2004 M9 earthquake at the western offshore of Aceh. This large destructive earthquake usually occurred at the shallow portion of the subduction zone between 10 – 35 km depth, while the intermediate-to-deep earthquake usually occurred at the greater depth, deeper than 65 km along the subduction, which produces small to moderate earthquake with a magnitude between M3-5. Thus, these deep events along the subduction zone usually being neglected. However, the recent study has shown that an anomalous large ground movement associated with a deep earthquake at the subduction zone has been observed along the forearc region while in the backarc or at its epicenter, it remains low. Hence, the characteristics of the body-wave at these regions are different, which could be utilized for hazard mitigation. For this reason, this study aims to identify the body-wave characteristics between the forearc and backarc regions at the Sumatra subduction zone. Several selected deep regional earthquake records with a depth greater than 100 km provided by the Agency for Meteorology, Climatology, and Geophysics of Indonesia (BMKG) were analyzed. The finding indicates that the body-waves recorded in the forearc region are significantly different, with the main characteristics are; 1. Amplitude: preserve high amplitude, 2. Arrival time: shows a delayed signal of P- and S-waves, and 3. Spectral: conserve energy at low to high frequency and shows as a dispersion. These findings suggest that the signal recorded at the forearc region travel within the subducting slab, and the late arrival of the signal indicates that the seismic waves record at forearc travel at the top of the subducting slab, i.e., the oceanic crust, which is having lower velocity to the surrounding mantle.
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Epicenter
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Seismotectonics
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The Spatial and Genetic Relation between Seismicity and Tectonic Trends, the Bitter Lakes Area, North-East Egypt The Bitter Lakes area was subjected to numerous seismic events which are genetically related to the well-known tectonic trends in NE Egypt. Based on the focal mechanism solutions and structural lineaments analysis, the spatial and genetic relationships of seismicity to these tectonic trends were clarified. The data set included eight focal mechanisms of recently recorded earthquakes that occurred during the period 1984–2003, and the structural lineaments extrtacted from the enhanced shaded relief image of the study area.
Lineament
North east
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