BEHIND VAN: TECTONIC STRESS CHANGES OR EARTHQUAKE INDUCED ALERTNESS?

Abstract Interferometric Synthetic Aperture Radar is an important tool for imaging surface deformation from large continental earthquakes. Here, we present maps of coseismic displacement and strain from the 2019 Ridgecrest earthquakes using multiple Sentinel-1 images. We provide three types of interferometric products. (1) Standard interferograms from two look directions provide an overview of the deformation and can be used for modeling coseismic slip. (2) Phase gradient maps from stacks of coseismic interferograms provide high-resolution (∼30 m) images of strain concentration and surface fracturing that can be used to guide field surveys. (3) High-pass filtered, stacked, unwrapped phase is decomposed into east–west and up–down, south–north components and is used to determine the sense of fault slip. The resulting phase gradient maps reveal over 300 surface fractures, including triggered slip on the Garlock fault. The east–west component of high-pass filtered phase reveals the polarity of the strike-slip offset (right lateral or left lateral) for many of the fractures. We find a small number of fractures that have slip polarity that is retrograde to the background tectonic stress. This is similar to observations of retrograde slip observed near the 1999 Mw 7.1 Hector Mine rupture, but the Ridgecrest observations are more completely imaged by the frequent and high-quality acquisitions from the twin Sentinel-1 spacecrafts. Determining whether the retrograde features are triggered slip on existing faults, or compliant fault deformation in response to stress changes from the Ridgecrest earthquakes, or new Coulomb-style failures, will require additional field work, modeling, and analysis.

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A modified Coulomb failure seismicity model to study earthquake occurrence and frequency-magnitude distributions

10.5194/egusphere-egu21-3176 ◽

2021 ◽

Author(s):

Torsten Dahm

Keyword(s):

Tectonic Stress ◽

Time Dependent ◽

New Model ◽

Coulomb Stress Changes ◽

Stress Effects ◽

Effective Media ◽

Aftershock Sequences ◽

Stress Changes ◽

Coulomb Failure ◽

Frequency Magnitude

The linear Coulomb failure (LCM) and the rate-and-state model (RSM) are two widely-used physics-based seismicity models both assuming Coulomb stress changes acting on pre-existing populations of faults. While both predict background earthquake rates and time-dependent stress effects, only the RSM can additionally explain the time-dependent triggering of aftershocks.We develop a modified effective media Coulomb model which accounts for the possibility of earthquake nucleation and retarded triggering of rupture. The new model has only two independent parameters and explains all statistical features of seismicity equally well as the RMS, but is simpler in its concept and provides insights in the possible nature of time-dependent frequency-magnitude distributions. Some of the statistical predictions are different compared to the RSM or LCM. For instance, the model domain is not limited to positive earthquake background or stressing rates; it can also simulate seismicity under zero stressing assumptions. The increase of background seismicity with tectonic stressing is nonlinear, different to the other models, and may even saturate if the tectonic stress loading is very strong. The Omori aftershock decay is predicted in the new model with an exponent of p=1 also for time periods much larger than the aftershock decay time, however, the productivity factor K is time dependent with a very slow exponential attenuation. The attenuation may explain the apparent variation of p in observed aftershock sequences. Interesting is also that the new model predicts a co-seismic peak of triggered aftershocks, which depends on the magnitude of the stress step and does not influence the attenuation of aftershocks following the stress step. It could be a physical explanation for the c-value in Omori&#8217;s law, the origin of which is still under discussion.We compare the new model to RSM and LCM and discuss the possible implications for earthquake clustering and frequency magnitude distributions.

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Deciphering the source parameters and genesis of the 2017, Mw 4 Montesano earthquake close to the Val d’Agri Oilfield (Italy)

10.5194/egusphere-egu21-1076 ◽

2021 ◽

Author(s):

José Ángel López-Comino ◽

Thomas Braun ◽

Torsten Dahm ◽

Simone Cesca ◽

Stefania Danesi

Keyword(s):

Moment Tensor ◽

Source Parameters ◽

Tectonic Stress ◽

Fault System ◽

S Waves ◽

Hydrocarbon Reservoir ◽

Empirical Green Function ◽

Stress Changes ◽

The Moment ◽

Directivity Effects

On October 27th, 2017, a Mw 4 earthquake occurred close to the municipality of Montesano sulla Marcellana, less than 10 km external to the concession of the largest European on-shore hydrocarbon reservoir - the Val d&#8217;Agri oilfield (Southern Italy). Being a weak event located outside the extended monitoring domain of the industrial concession, the relevance of this earthquake and possible links with the hydrocarbon exploitation were not deepened. The study of weak to moderate earthquakes can improve the characterization of the potentially destructive seismic hazard of this particular area, already struck by M>6.5 episodes in the past. Taking advantage of a wide coverage of seismic stations deployed in the VA region, we analyze the source parameters of this Mw 4 earthquake applying advanced seismological techniques to estimate the uncertainties derived from the moment tensor inversion and identify plausible directivity effects. The moment tensor is dominated by a NW-SE oriented normal faulting with a centroid depth of 14 km. A single ML 2.1 aftershock was recorded and used as empirical Green function to calculate the apparent source time function for the mainshock. Apparent durations (in the range 0.11 - 0.21 s, obtained from S-waves) define an azimuthal pattern which reveals an asymmetric bilateral rupture with the 70% of the rupture propagation in the N310&#176;W direction, suggesting a rupture plane dipping to the SW. Our results conclude that the Montesano earthquake activated a deeper fault segment associated to the Eastern Agri Fault System close to the basement. The relative low trigger potential below 10% based on depletion-induced stress changes discards an induced or triggered event due to the long-term hydrocarbon extraction in the Val d&#8217;Agri oilfield, and it rather suggests a natural cause due to the local tectonic stress.

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Preliminary study of stress changes evolution on central part of Sumatran Fault influenced by large interplate earthquakes and tectonic stress rates

IOP Conference Series Earth and Environmental Science ◽

10.1088/1755-1315/873/1/012011 ◽

2021 ◽

Vol 873 (1) ◽

pp. 012011

Author(s):

Muhammad Taufiq Rafie ◽

Phil R Cummins ◽

David P Sahara ◽

Sri Widiyantoro ◽

Wahyu Triyoso ◽

...

Keyword(s):

Plate Boundary ◽

Tectonic Stress ◽

Stress Rate ◽

Intraplate Earthquakes ◽

Physical Mechanisms ◽

Stress Changes ◽

Almost All ◽

Short Time ◽

Sumatran Fault ◽

Interplate Earthquakes

Abstract The inland seismic activity in Great Sumatran Fault (GSF) has significantly increased over the past several decades after the occurrence of historical large interplate earthquakes along the plate boundary. This condition led to some occurrences of historical intraplate earthquakes along Sumatran fault. To quantitatively examine the physical mechanisms between intraplate earthquakes and interplate earthquakes, we estimated the static coseismic stress changes of Coulomb failure function (ΔCFF) using receiver fault approach from large historical-recorded interplate earthquakes and the increase in tectonic stress rates. We examined this research in the central part of GSF since this zone is assumed to have the most heterogeneous stress field and thus became our focus study area. The cumulative ΔCFF models showed almost all segments in the central part of GSF suffered negative changes (<-0.1 MPa) which assumed to be unlikely to rupture in short time. However, the preliminary analysis of the increase in tectonic stress rate indicated that large intraplate earthquakes occurred on Angkola and Siulak segments were dominantly influenced by the increase in interseismic stress rate just after the series of large subduction earthquake occurrences, apart from the decreased stress changes from those major interplate earthquakes.

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Stress Accumulation and Earthquake Activity on the Great Sumatran Fault, Indonesia

10.21203/rs.3.rs-1195020/v1 ◽

2022 ◽

Author(s):

Muhammad Taufiq Rafie ◽

David P. Sahara ◽

Phil R. Cummins ◽

Wahyu Triyoso ◽

Sri Widiyantoro

Keyword(s):

Time Evolution ◽

Slip Rate ◽

Tectonic Stress ◽

Coulomb Stress ◽

Earthquake Activity ◽

Coulomb Stress Changes ◽

Megathrust Earthquakes ◽

Stress Changes ◽

Sumatran Fault ◽

Stress Accumulation

Abstract The seismically active Sumatra subduction zone has generated some of the largest earthquakes in the instrumental record, and both historical accounts and paleogeodetic coral studies indicate such activity has historical recorded megathrust earthquakes and transferred stress to the surrounding, including the Great Sumatran Fault (GSF). Therefore, evaluating the stress transfer from these large subduction earthquakes could delineate the highly stressed area as potential-earthquake region along the GSF. In this study, we investigated eight megathrust earthquakes from 1797 to 2010 and resolved the accumulated Coulomb stress changes onto the 18 segments along the GSF. Additionally, we also estimated the rate of tectonic stress on the GSF segments which experienced large earthquake using the case of: (1) no sliver movement and (2) with sliver movement. Based on the historical stress changes of large earthquakes and the increase in tectonic stress rate, we analysed the historical stress changes time evolution on the GSF. The Coulomb stress accumulation of megathrust earthquakes between 1797-1907 increase the stress changes mainly on the southern part of GSF which followed by four major events between 1890-1943. The estimation of tectonic stress rates using case (1) produces low rate and long recurrence intervals which implies that the megathrust earthquakes plays an important role in allowing the GSF earthquake to occur. When implementing the arc-parallel sliver movement of case (2) to the calculation, the tectonic stress rates is 9 to 58 times higher than case (1) of no sliver movement. The observed slip rate of 15-16 mm/yr at the GSF is consistent with the recurrence interval for full-segment rupture of 100-200 years obtained from case (2). This suggests that the GSF earthquake is more controlled by the rapid arc-parallel forearc sliver motion. Furthermore, the analysis of stress changes time evolution model shows that some segments such as Tripa (North and South), Angkola, Musi and Manna appear to be brought back in their seismic cycles since these segments have experienced full-segment rupture and likely locked, increasing their earthquake hazard potentials.

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Interaction Between Historical Earthquakes and the 2021 Mw7.4 Maduo Event and Their Impacts on the Seismic Gap Areas Along the East Kunlun Fault

10.21203/rs.3.rs-934288/v1 ◽

2021 ◽

Author(s):

Peiyu Dong ◽

Bin Zhao ◽

Xuejun Qiao

Keyword(s):

Source Area ◽

Historical Earthquakes ◽

Tectonic Stress ◽

Inhibitory Effect ◽

Seismic Gap ◽

Seismogenic Fault ◽

Qinghai Province ◽

Coulomb Stress Changes ◽

Stress Shadow ◽

Stress Changes

Abstract On May 21, 2021 (UTC time), a Mw7.4 earthquake struck Maduo County, Qinghai Province, China. The rupture of this typical strike-slip event and its aftershocks along the Kunlun-Jiangcuo fault (JCF) propagated approximately 170 km from the epicenter. In this study, we calculated the coseismic and postseismic Coulomb stress changes induced by 14 historical earthquakes and investigated their impacts on the 2021 Maduo source area. We found that the JCF is in the stress shadow of these historical events with a combined ΔCFS range of approximately -0.4 to -0.2 MPa. Since the seismogenic fault of the 1937 event is nearly parallel and close to the JCF, the rupture of the 1937 event had the greatest inhibitory effect on Maduo source area. We hypothesize that the actual loading rate at the depth of the seismogenic layer in the Maduo source area is much higher than the simulated value (0.3 kPa/a). Consequently, the Maduo earthquake still occurred despite the considerable delaying effect of these historical earthquakes (especially the 1937 event). Our findings also indicate that the tectonic stress in the eastern Bayanhar block is still rapidly accumulating and adjusting. Our investigation further reveals the enhanced stress induced by the historical and Maduo events with ΔCFS values of approximately 30~300 kPa and 50~300 kPa on the XDS and the eastern end of the EKF, respectively, not only on the MMS but also at the eastern end of each branch segment of the EKF. Hence, considering the accumulation of tectonic stress, we suggest that the seismic hazard in these two regions has been promoted.

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STRESS INTERACTION BETWEEN THRUST FAULTS ALONG THE SW HELLENIC ARC (GREECE)

Bulletin of the Geological Society of Greece ◽

10.12681/bgsg.16625 ◽

2018 ◽

Vol 40 (1) ◽

pp. 386

Author(s):

A. Messini ◽

E. E. Papadimitriou ◽

V. G. Karakostas ◽

I. Baskoutas

Keyword(s):

Tectonic Stress ◽

Elastic Half Space ◽

Coulomb Stress ◽

Thrust Faults ◽

Tectonic Plates ◽

Coulomb Stress Changes ◽

Seismic Slip ◽

Hellenic Arc ◽

Stress Changes ◽

Major Fault

The occurrence of strong earthquakes (M>6.3) and the evolution of the stress field along the southwestern part of the Hellenic arc since 1959 are examined by the calculation of Coulomb stress changes. The study area is characterized by low angle thrust faults and high seismicity as being part of the subduction interface. Coulomb stress changes were calculated assuming that earthquakes can be modeled as static dislocations in an elastic half-space, considering the co-seismic slip during strong events and the slow tectonic stress build-up along major fault segments due to the movements of the tectonic plates. The ruptures are modeled taking into account the strike, dip, and rake appropriate to each event examined. It is evaluated whether the stress changes brought a given earthquake closer to, or farther away from, failure. It was found that the majority of the events (strong and smaller) are located in stress enhanced areas.

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