scholarly journals Source mechanisms of laboratory earthquakes during fault nucleation and formation

2021 ◽  
Author(s):  
Thomas King ◽  
Sergio Vinciguerra ◽  
Jodi Burgess ◽  
Philip Benson ◽  
Luca De Siena
Keyword(s):  
Source Mechanisms ◽  
Fault Nucleation

Dense surface seismic data confirm non-double-couple source mechanisms induced by hydraulic fracturing

Geophysics ◽  
2016 ◽  
Vol 81 (6) ◽  
pp. KS207-KS217 ◽  
Author(s):  
Jeremy D. Pesicek ◽  
Konrad Cieślik ◽  
Marc-André Lambert ◽  
Pedro Carrillo ◽  
Brad Birkelo
Keyword(s):  
Hydraulic Fracturing ◽  
Seismic Data ◽  
P Wave ◽  
Source Modeling ◽  
Moment Tensors ◽  
Amplitude Data ◽  
Double Couple ◽  
Source Mechanisms ◽  
Source Models ◽  
Favorable Conditions

We have determined source mechanisms for nine high-quality microseismic events induced during hydraulic fracturing of the Montney Shale in Canada. Seismic data were recorded using a dense regularly spaced grid of sensors at the surface. The design and geometry of the survey are such that the recorded P-wave amplitudes essentially map the upper focal hemisphere, allowing the source mechanism to be interpreted directly from the data. Given the inherent difficulties of computing reliable moment tensors (MTs) from high-frequency microseismic data, the surface amplitude and polarity maps provide important additional confirmation of the source mechanisms. This is especially critical when interpreting non-shear source processes, which are notoriously susceptible to artifacts due to incomplete or inaccurate source modeling. We have found that most of the nine events contain significant non-double-couple (DC) components, as evident in the surface amplitude data and the resulting MT models. Furthermore, we found that source models that are constrained to be purely shear do not explain the data for most events. Thus, even though non-DC components of MTs can often be attributed to modeling artifacts, we argue that they are required by the data in some cases, and can be reliably computed and confidently interpreted under favorable conditions.

Estimation of DAS microseismic source mechanisms using unsupervised deep learning

2021 ◽  
Author(s):  
Matthew Eaid ◽  
Chaoshun Hu ◽  
Lin Zhang ◽  
Scott Keating ◽  
Kristopher Innanen
Keyword(s):  
Deep Learning ◽  
Source Mechanisms ◽  
Unsupervised Deep Learning

Determination of point source mechanisms

2014 ◽  
pp. 108-134 ◽  
Author(s):  
Agustin Udias ◽  
Raul Madariaga ◽  
Elisa Buforn
Keyword(s):  
Point Source ◽  
Source Mechanisms

scholarly journals Is the Eastern Denali fault still active?

Geology ◽  
2021 ◽  
Author(s):  
Minhee Choi ◽  
David W. Eaton ◽  
Eva Enkelmann
Keyword(s):  
Bering Sea ◽  
Active Fault ◽  
Strike Slip ◽  
Historical Seismicity ◽  
Fault System ◽  
Denali Fault ◽  
Regional Deformation ◽  
Source Mechanisms ◽  
Structural Boundary ◽  
The Bering Sea

The Denali fault, a transcurrent fault system that extends from northwestern Canada across Alaska toward the Bering Sea, is partitioned into segments that exhibit variable levels of historical seismicity. A pair of earthquakes (M 6.2 and 6.3) on 1 May 2017, in proximity to the Eastern Denali fault (EDF), exhibited source mechanisms and stress conditions inconsistent with expectations for strike-slip fault activation. Precise relocation of ~1500 aftershocks revealed distinct fault strands that are oblique to the EDF. Calculated patterns of Coulomb stress show that the first earthquake likely triggered the second one. The EDF parallels the Fairweather transform, which separates the obliquely colliding Yakutat microplate from North America. In our model, inboard transfer of stress is deforming and shortening the mountainous region between the EDF and the Fairweather transform. This is supported by historical seismicity concentrated southwest of the EDF, suggesting that it now represents a structural boundary that controls regional deformation but is no longer an active fault.

scholarly journals Characteristics of local earthquake seismograms of varying dislocation sources in a stratified upper crust and modeling for P and S velocity structure: comparison with observations in the Koyna-Warna region, India

2016 ◽  
Vol 58 (6) ◽  
Author(s):  
V. G. Krishna
Keyword(s):  
Velocity Structure ◽  
Source Parameters ◽  
Velocity Model ◽  
Strike Slip ◽  
Synthetic Seismograms ◽  
Structure Comparison ◽  
Earthquake Sources ◽  
Crustal Velocity ◽  
Source Mechanisms ◽  
Local Earthquake

<p>Vertical component record sections of local earthquake seismograms from a state-of-the-art Koyna-Warna digital seismograph network are assembled in the reduced time versus epicentral distance frame, similar to those obtained in seismic refraction profiling. The record sections obtained for an average source depth display the processed seismograms from nearly equal source depths with similar source mechanisms and recorded in a narrow azimuth range, illuminating the upper crustal P and S velocity structure in the region. Further, the seismogram characteristics of the local earthquake sources are found to vary significantly for different source mechanisms and the amplitude variations exceed those due to velocity model stratification. In the present study a large number of reflectivity synthetic seismograms are obtained in near offset ranges for a stratified upper crustal model having sharp discontinuities with 7%-10% velocity contrasts. The synthetics are obtained for different source regimes (e.g., strike-slip, normal, reverse) and different sets of source parameters (strike, dip, and rake) within each regime. Seismogram sections with dominantly strike-slip mechanism are found to be clearly favorable in revealing the velocity stratification for both P and S waves. In contrast the seismogram sections for earthquakes of other source mechanisms seem to display the upper crustal P phases poorly with low amplitudes even in presence of sharp discontinuities of high velocity contrasts. The observed seismogram sections illustrated here for the earthquake sources with strike-slip and normal mechanisms from the Koyna-Warna seismic region substantiate these findings. Travel times and reflectivity synthetic seismograms are used for 1-D modeling of the observed virtual source local earthquake seismogram sections and inferring the upper crustal velocity structure in the Koyna-Warna region. Significantly, the inferred upper crustal velocity model in the region reproduces the synthetic seismograms comparable to the observed sections for earthquake sources with differing mechanisms in the Koyna and Warna regions.</p>

scholarly journals The seisniicity of Iran. The Silakhor (Luristan) earthquake of 23rd Ianuary, 1909 (Part II)

2010 ◽  
Vol 27 (3-4) ◽  
Author(s):  
N. N. AMBRASEYS
Keyword(s):  
Tectonic Activity ◽  
The World ◽  
Source Mechanisms ◽  
The Difference ◽  
Large Earthquakes ◽  
Remote Part

This paper shows t h a t given certain conditions it is perfectly feasible to study an earthquake that occurred three-quarters of a century ago in a remote part of the world. Also, it shows that there are many large earthquakes which, because of lack of interdisciplinary efforts to study such events, have remained hitherto little known or totally unknown. The case of the Silakhor earthquake revealed deficiencies in the determination of epicentres by ISS and Gutenberg; the difference between macroseismic and instrumental position for the Silakhor earthquake is 380 kilometres, a difference which lias caused a serious problem in the assessment of seisniicity of Iran. Accurate macroseismic d a t a may be used to minimize bias in t h e instrumental relocation of the larger events and to study source mechanisms. Untili this study was undertaken, the faulting associated with the Silakhor earthquake was totally unknown. Even more important t h a n the value of recent faulting for its significance in resolving ambiguities in t h e choice of the t r u e source parametres, is the information that can be gleaned from evidence for the mechanism of earthquakes that occurred long before t h e advent of modern seismology and in particular, for the pattern of recent tectonic activity.

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