scholarly journals Centroid Moment Tensor of the 2019 MW 5.7 Changning Earthquake Refined Using 3D Green’s Functions Considering Surface Topography

2021 ◽  
Vol 9 ◽  
Author(s):  
Yuanhang Huo ◽  
Wei Zhang ◽  
Jie Zhang
Keyword(s):  
Green's Functions ◽  
3D Model ◽  
Green’S Functions ◽  
Moment Tensor ◽  
Nodal Plane ◽  
Centroid Moment Tensor ◽  
Event Location ◽  
Source Mechanisms ◽  
1D Model ◽  
Rugged Topography

The MW 5.7 Changning earthquake occurred in southern Sichuan basin on 17 June 2019 and was the largest event ever recorded in this region. There are still some arguments existing about the causes of the earthquake and its possible links with water injections. Many studies on this earthquake have been performed, but the event depths obtained among them are significantly different and the source mechanisms also exhibit variations. In this study, we design an inversion scheme and use 3D Green’s functions considering the rugged topography of this region to determine the event location and moment tensor of the Changning earthquake based on waveform fittings. The 3D model can reduce the uncertainty due to the approximation of 1D model and better constrain the solutions. The latitude and the longitude of event location are 28.34°N and 104.82°E respectively and the depth is 3.14 km. The nodal plane solutions are strike 295°/dip 88°/rake 14° and strike 204°/dip 76°/rake 178°. The percentages of DC, CLVD and ISO components are 10, −83, and −7%, respectively. The good waveform fittings at 17 broadband stations indicate the reliability of the source mechanism in this study.

Multievent moment-tensor inversion for ill-conditioned geometries

Geophysics ◽  
2016 ◽  
Vol 81 (2) ◽  
pp. KS11-KS24 ◽  
Author(s):  
Xin Yu ◽  
Scott Leaney ◽  
Jim Rutledge ◽  
Chris Chapman
Keyword(s):  
Moment Tensor ◽  
Moment Tensor Inversion ◽  
Data Set ◽  
Data Noise ◽  
Monitoring Wells ◽  
Monitoring Well ◽  
Location Uncertainty ◽  
Event Location ◽  
Source Mechanisms ◽  
Scalar Moment

Moment-tensor inversion under single monitoring well geometries becomes unstable due to the singularity of the inversion matrix. But microseismic events observed during hydraulic fracturing commonly show clusters of events with similar source mechanisms despite differences in the origin time and the magnitude. If the events with similar source mechanisms can be grouped and inverted for a single common moment tensor, the singularity can be eliminated. We have developed a normalized multievent moment-tensor inversion (NME-MTI) method, which does the MTI simultaneously for multiple events, to test the feasibility of this multievent approach. First, the scalar moment for each event was estimated using the far-field low-frequency level at each receiver. Then, the displacements measured at the receivers were normalized by the scalar moment and used to invert for the common moment tensor simultaneously for all the events in the group. We introduced a gradient search method to minimize the overall misfit by adjusting the scalar moment for each event to reduce the errors introduced by the scalar moment estimation. The algorithm was tested with a synthetic data set with four monitoring wells and a field data set with dual monitoring wells. It was proved that the NME-MTI method can retrieve the moment tensors of the event groups with data from a single monitoring well. The effects of uncertainties on the inversion were examined with data noise, scalar moment uncertainty, and event location uncertainty. The results showed that the ME-MTI result is much less sensitive to the data noise and the scalar moment uncertainty than the single-event approach. The results also determined that although the bias to the solutions increases when the event location uncertainty increases, the bias can be controlled by reducing the event location uncertainties using a more accurate location algorithm.

Uncertainties in Seismic Moment Tensors Inferred from Differences between Global Catalogs

2021 ◽  
Author(s):  
Boris Rösler ◽  
Seth Stein ◽  
Bruce D. Spencer
Keyword(s):  
Moment Tensor ◽  
Centroid Moment Tensor ◽  
Moment Tensors ◽  
Double Couple ◽  
Source Mechanisms ◽  
Order Of Magnitude ◽  
The Difference ◽  
The Moment ◽  
Source Geometry ◽  
Scalar Moment

Abstract Catalogs of moment tensors form the foundation for a wide variety of seismological studies. However, assessing uncertainties in the moment tensors and the quantities derived from them is difficult. To gain insight, we compare 5000 moment tensors in the U.S. Geological Survey (USGS) and the Global Centroid Moment Tensor (Global CMT) Project catalogs for November 2015–December 2020 and use the differences to illustrate the uncertainties. The differences are typically an order of magnitude larger than the reported errors, suggesting that the errors substantially underestimate the uncertainty. The catalogs are generally consistent, with intriguing differences. Global CMT generally reports larger scalar moments than USGS, with the difference decreasing with magnitude. This difference is larger than and of the opposite sign from what is expected due to the different definitions of the scalar moment. Instead, the differences are intrinsic to the tensors, presumably in part due to different phases used in the inversions. The differences in double-couple components of source mechanisms and the fault angles derived from them decrease with magnitude. Non-double-couple (NDC) components decrease somewhat with magnitude. These components are moderately correlated between catalogs, with correlations stronger for larger earthquakes. Hence, small earthquakes often show large NDC components, but many have large uncertainties and are likely to be artifacts of the inversion. Conversely, larger earthquakes are less likely to have large NDC components, but these components are typically robust between catalogs. If so, these can indicate either true deviation from a double couple or source complexity. The differences between catalogs in scalar moment, source geometry, or NDC fraction of individual earthquakes are essentially uncorrelated, suggesting that the differences reflect the inversion rather than the source process. Despite the differences in moment tensors, the location and depth of the centroids are consistent between catalogs. Our results apply to earthquakes after 2012, before which many moment tensors were common to both catalogs.

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