scholarly journals Energy-based average stress drop and its uncertainty during the 2015 Mw 7.8 Nepal earthquake constrained by geodetic data and its implications to earthquake dynamics

2019 ◽  
Vol 217 (2) ◽  
pp. 784-797 ◽  
Author(s):  
Mareike Adams ◽  
Jinlai Hao ◽  
Chen Ji
Keyword(s):  
Stress Drop ◽  
Geodetic Data ◽  
Average Stress ◽  
Earthquake Dynamics ◽  
Nepal Earthquake

scholarly journals Stress Drop, Seismogenic Index and Fault Cohesion of Fluid-Induced Earthquakes

2021 ◽  
Author(s):  
Serge A. Shapiro ◽  
Carsten Dinske
Keyword(s):  
Stress Drop ◽  
Induced Seismicity ◽  
Quantitative Characteristic ◽  
High Stress ◽  
Operation Time ◽  
Average Stress ◽  
Induced Earthquakes ◽  
Effective Stresses ◽  
Seismicity Rates

AbstractSometimes, a rather high stress drop characterizes earthquakes induced by underground fluid injections or productions. In addition, long-term fluid operations in the underground can influence a seismogenic reaction of the rock per unit volume of the fluid involved. The seismogenic index is a quantitative characteristic of such a reaction. We derive a relationship between the seismogenic index and stress drop. This relationship shows that the seismogenic index increases with the average stress drop of induced seismicity. Further, we formulate a simple and rather general phenomenological model of stress drop of induced earthquakes. This model shows that both a decrease of fault cohesion during the earthquake rupture process and an enhanced level of effective stresses could lead to high stress drop. Using these two formulations, we propose the following mechanism of increasing induced seismicity rates observed, e.g., by long-term gas production at Groningen. Pore pressure depletion can lead to a systematic increase of the average stress drop (and thus, of magnitudes) due to gradually destabilizing cohesive faults and due to a general increase of effective stresses. Consequently, elevated average stress drop increases seismogenic index. This can lead to seismic risk increasing with the operation time of an underground reservoir.

scholarly journals The stop-start control of seismicity by fault bends along the Main Himalayan Thrust

2021 ◽  
Vol 2 (1) ◽  
Author(s):  
Sharadha Sathiakumar ◽  
Sylvain Barbot
Keyword(s):  
Seismic Hazards ◽  
Geodetic Data ◽  
Source Mechanism ◽  
Seismogenic Zone ◽  
Seismic Cycle ◽  
Rupture Propagation ◽  
Alternative Models ◽  
Nepal Earthquake

AbstractThe Himalayan megathrust accommodates most of the relative convergence between the Indian and Eurasian plates, producing cycles of blind and surface-breaking ruptures. Elucidating the mechanics of down-dip segmentation of the seismogenic zone is key to better determine seismic hazards in the region. However, the geometry of the Himalayan megathrust and its impact on seismicity remains controversial. Here, we develop seismic cycle simulations tuned to the seismo-geodetic data of the 2015 Mw 7.8 Gorkha, Nepal earthquake to better constrain the megathrust geometry and its role on the demarcation of partial ruptures. We show that a ramp in the middle of the seismogenic zone is required to explain the termination of the coseismic rupture and the source mechanism of up-dip aftershocks consistently. Alternative models with a wide décollement can only explain the mainshock. Fault structural complexities likely play an important role in modulating the seismic cycle, in particular, the distribution of rupture sizes. Fault bends are capable of both obstructing rupture propagation as well as behave as a source of seismicity and rupture initiation.

Improved approach for stress drop estimation and its application to an induced earthquake sequence in Oklahoma

2020 ◽  
Vol 223 (1) ◽  
pp. 233-253
Author(s):  
X Chen ◽  
R E Abercrombie
Keyword(s):  
Stress Drop ◽  
Source Parameters ◽  
High Stress ◽  
Temporal Variations ◽  
Earthquake Source ◽  
Average Stress ◽  
Corner Frequency ◽  
Resolution Limit ◽  
Spectral Fitting ◽  
Spatio Temporal

SUMMARY We calculate source parameters for fluid-injection induced earthquakes near Guthrie, Oklahoma, guided by synthetic tests to quantify uncertainties. The average stress drop during an earthquake is a parameter fundamental to ground motion prediction and earthquake source physics, but it has proved hard to measure accurately. This has limited our understanding of earthquake rupture, as well as the spatio-temporal variations of fault strength. We use synthetic tests based on a joint spectral-fitting method to define the resolution limit of the corner frequency as a function of the maximum frequency of usable signal, for both individual spectra and the average from multiple stations. Synthetic tests based on stacking analysis find that an improved stacking approach can recover the true input stress drop if the corner frequencies are within the resolution limit defined by joint spectral-fitting. We apply the improved approach to the Guthrie sequence, using different wave types and signal-to-noise criteria to understand the stability of the calculated stress drop values. The results suggest no systematic scaling relationship of stress drop for M ≤ 3.1 earthquakes, but larger events (M ≥ 3.5) tend to have higher average stress drops. Some robust spatio-temporal variations can be linked to the triggering processes and indicate possible stress heterogeneity within the fault zone. Tight clustering of low stress drop events at the beginning stage of the sequence suggests that pore pressure influences earthquake source processes. Events at shallow depth have lower stress drop compared to deeper events. The largest earthquake occurred within a cluster of high stress drop events, likely rupturing a strong asperity.

scholarly journals Earthquake Seismic Moment, Rupture Radius and Stress-drop from P-wave Displacement Amplitude vs Time Curves

2021 ◽  
Author(s):  
aldo zollo ◽  
sahar nazeri ◽  
Simona Colombelli
Keyword(s):  
Stress Drop ◽  
Seismic Moment ◽  
Central Italy ◽  
Average Stress ◽  
Displacement Amplitude ◽  
P Wave ◽  
Parametric Modelling ◽  
Peak Displacement ◽  
Reliable Determination ◽  
Anelastic Attenuation

The reliable determination of earthquake source parameters is a relevant task of seismological investigations which ground nowadays on high quality seismic waveforms collected by near-source dense arrays of ground motion sensors. Here we propose a parametric modelling technique which analyzes the time-domain P-wave signal recorded in the near-source range of small-to-large size earthquakes. Assuming a triangular moment-rate function and a uniform speed, circular rupture model, we develop the equations to estimate the seismic moment, rupture radius and stress-drop from the corner-time and plateau level of the average logarithm of the P-wave displacement vs time curves (LPDT). The constant-Q, anelastic attenuation effect is accounted by a post-processing procedure that evaluates the Q-unperturbed moment-rate triangular shape.<br>The methodology has been validated through the application to the acceleration records of the 2016-2017 Central Italy and 2007-2019 Japan earthquake sequences covering a wide moment magnitude range (Mw 2.5 - 6.5) and recording distance < 100 km. After correcting for the anelastic attenuation function, the estimated average stress-drop and the confidence interval (〈∆σ〉=0.60 (0.42-0.87) MPa and 〈∆σ〉=1.53 (1.01-2.31) for crustal and subcrustal events of Japan and 〈∆σ〉=0.36(0.30-0.44) MPa for Central Italy) show, for both regions, a self-similar, constant stress-drop scaling of the rupture duration/radius with seismic moment. The smaller sensitivity of the spatially averaged, time-varying peak displacement amplitude to the radiation from localized high slip patch on the fracture surface, could explain the retrieved smaller average stress-drops for sub-crustal earthquakes in Japan and M>5.5 events in Central Italy relative to previous estimates using spectral methods.<br><br>

scholarly journals Earthquake Seismic Moment, Rupture Radius and Stress-drop from P-wave Displacement Amplitude vs Time Curves

2021 ◽  
Author(s):  
aldo zollo ◽  
sahar nazeri ◽  
Simona Colombelli
Keyword(s):  
Stress Drop ◽  
Seismic Moment ◽  
Central Italy ◽  
Average Stress ◽  
Displacement Amplitude ◽  
P Wave ◽  
Parametric Modelling ◽  
Peak Displacement ◽  
Reliable Determination ◽  
Anelastic Attenuation

The reliable determination of earthquake source parameters is a relevant task of seismological investigations which ground nowadays on high quality seismic waveforms collected by near-source dense arrays of ground motion sensors. Here we propose a parametric modelling technique which analyzes the time-domain P-wave signal recorded in the near-source range of small-to-large size earthquakes. Assuming a triangular moment-rate function and a uniform speed, circular rupture model, we develop the equations to estimate the seismic moment, rupture radius and stress-drop from the corner-time and plateau level of the average logarithm of the P-wave displacement vs time curves (LPDT). The constant-Q, anelastic attenuation effect is accounted by a post-processing procedure that evaluates the Q-unperturbed moment-rate triangular shape.<br>The methodology has been validated through the application to the acceleration records of the 2016-2017 Central Italy and 2007-2019 Japan earthquake sequences covering a wide moment magnitude range (Mw 2.5 - 6.5) and recording distance < 100 km. After correcting for the anelastic attenuation function, the estimated average stress-drop and the confidence interval (〈∆σ〉=0.60 (0.42-0.87) MPa and 〈∆σ〉=1.53 (1.01-2.31) for crustal and subcrustal events of Japan and 〈∆σ〉=0.36(0.30-0.44) MPa for Central Italy) show, for both regions, a self-similar, constant stress-drop scaling of the rupture duration/radius with seismic moment. The smaller sensitivity of the spatially averaged, time-varying peak displacement amplitude to the radiation from localized high slip patch on the fracture surface, could explain the retrieved smaller average stress-drops for sub-crustal earthquakes in Japan and M>5.5 events in Central Italy relative to previous estimates using spectral methods.<br><br>

Characterization of Major Fault Systems in the Kachchh Intraplate Region, Gujarat, India, by Focal Mechanism and Source Parameters

2020 ◽  
Vol 91 (6) ◽  
pp. 3496-3517
Author(s):  
Charu Kamra ◽  
Sumer Chopra ◽  
Ram Bichar Singh Yadav ◽  
Vishwa Joshi
Keyword(s):  
Focal Mechanism ◽  
Stress Drop ◽  
Source Parameters ◽  
Strike Slip ◽  
Average Stress ◽  
Fault System ◽  
Rift Basin ◽  
Fault Systems ◽  
Major Fault

Abstract The focal mechanism and source parameters of 41 local earthquakes (Mw 4.0–5.1) that occurred in the Kachchh rift basin, which is seismically one of India’s most active intraplate regions, are determined to characterize various active fault systems in that region. The tectonics in the rift basin are heterogeneous and complex. In the present study, it was found that one-third of the earthquakes exhibit reverse mechanism and three-fourth are either strike slip or have some components of strike slip. Thus, we conclude that transverse tectonics are currently dominant in the Kachchh rift. These transverse faults are preferably oriented in the northeast–southwest and northwest–southeast directions in the eastern and western parts of the rift, respectively. The movement is sinistral and dextral on faults that are oriented in the northeast–southwest and northwest–southeast directions, respectively. These transverse faults are almost vertical (dip&gt;70°) and mostly blind with no surface expressions. Most of the significant faults that strike east–west dip toward the south and are listric. The stress drop of these 41 earthquakes ranges between 2.3 and 10.39 MPa. It was found that the stress drop of earthquakes may depend on the focal mechanism and is independent of focal depths. The average stress drop is found to be the highest (7.3 MPa) for the earthquakes that show a dominant normal mechanism accompanied by strike slip (5.4 MPa) and reverse (4.7 MPa). The average stress drop of the Kachchh intraplate region is 5.3 MPa, which is consistent with other intraplate regions of the world. A conceptual model of the fault system in the Kachchh region is proposed, based on the results obtained in the present study.

A high-frequency magnitude scale

1995 ◽  
Vol 85 (3) ◽  
pp. 825-833
Author(s):  
Gail M. Atkinson ◽  
Thomas C. Hanks
Keyword(s):  
North America ◽  
Ground Motion ◽  
Stress Drop ◽  
High Frequency ◽  
Ground Motions ◽  
Amplitude Spectrum ◽  
Average Stress ◽  
Magnitude Scale ◽  
Eastern North America ◽  
Frequency Magnitude

Abstract A high-frequency magnitude scale (m) is proposed: m=2log⁡a˜hf+3, where ãhf is the high-frequency level of the Fourier amplitude spectrum of acceleration in cm/sec (average or random horizontal component), at a hypocentral or closest fault distance of 10 km. m can be determined from either instrumental data or the felt area of an earthquake. The definition of m has been arranged such that m = M (moment magnitude) for events of “average” stress drop, in both eastern North America (ENA) and California. m provides a measure of the stress drop if M is also known. The observed relationship between m and M indicates that the average stress drop is about 150 bars for ENA earthquakes, and about 70 bars for California earthquakes. The variability of stress drop is much larger in ENA than in California. The chief justification for the m scale is its utility in the interpretation of the large preinstrumental earthquakes that are so important to seismic hazard estimation in eastern North America. For such events, m can be determined more reliably than can M or mN (Nuttli magnitude), and forms a much better basis for estimating high-frequency ground motions. When used as a pair, m and M provide a good index of ground motion over the entire engineering frequency band. If both of these magnitudes can be defined for an earthquake then a ground-motion model, such as the stochastic model, can be used to obtain reliable estimates of response spectra and peak ground motions.

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