Focal mechanism and stress field in the northeastern Tibetan Plateau: insight into layered crustal deformations

2019 ◽  
Vol 218 (3) ◽  
pp. 2066-2078 ◽  
Author(s):  
Cunrui Han ◽  
Zhouchuan Huang ◽  
Mingjie Xu ◽  
Liangshu Wang ◽  
Ning Mi ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
Stress Field ◽  
Focal Mechanism ◽  
Horizontal Stress ◽  
P Wave ◽  
The Tibetan Plateau ◽  
Linear Inversion ◽  
Focal Mechanism Solutions ◽  
Stress Orientations ◽  
Ne Tibetan Plateau

SUMMARY Focal mechanism solutions (FMSs) reflect the stress field underground directly. They provide essential clue for crustal deformations and therefore improve our understanding of tectonic uplift and expansion of the Tibetan Plateau. In this study, we applied generalized Cut and Paste and P-wave first-motion methods to determine 334 FMSs (2.0 ≤ Mw ≤ 6.4) with the data recorded by a new temporary network deployed in the NE Tibetan Plateau by ChinArray project. We then used 1015 FMSs (including 681 published FMSs) to calculate the regional stress field with a damped linear inversion. The results suggest dominant thrust and strike-slip faulting environments in the NE Tibetan Plateau. From the Qilian thrust belt to the Qinling orogen, the maximum horizontal stress orientations (${S_\mathrm{ H}}$) rotate clockwise from NNE to NE, and further to EW, showing a fan-shaped pattern. The derived minimum horizontal stress orientations (${S_\mathrm{ h}}$) are parallel to the aligned fabrics in the mantle lithosphere indicated by shear wave splitting measurements, suggesting vertically coherent deformation in the NE Tibetan Plateau. Beneath the SW Qinling adjacent to the plateau, however, the stress orientations in the shallow and deep crust are different, whereas the deep crustal stress field indicates possible ductile crustal flow or shear.

PRESENT-DAY STATE-OF-STRESS OF SOUTHEAST AUSTRALIA

2006 ◽  
Vol 46 (1) ◽  
pp. 283 ◽  
Author(s):  
E. Nelson ◽  
R. Hillis ◽  
M. Sandiford ◽  
S. Reynolds ◽  
S. Mildren
Keyword(s):  
Focal Mechanism ◽  
Horizontal Stress ◽  
Strike Slip ◽  
Focal Mechanism Solutions ◽  
Southeast Australia ◽  
State Of Stress ◽  
Earthquake Focal Mechanism ◽  
Minimum Horizontal Stress ◽  
Maximum Horizontal Stress ◽  
Gippsland Basin

There have been several studies, both published and unpublished, of the present-day state-of-stress of southeast Australia that address a variety of geomechanical issues related to the petroleum industry. This paper combines present-day stress data from those studies with new data to provide an overview of the present-day state-of-stress from the Otway Basin to the Gippsland Basin. This overview provides valuable baseline data for further geomechanical studies in southeast Australia and helps explain the regional controls on the state-of-stress in the area.Analysis of existing and new data from petroleum wells reveals broadly northwest–southeast oriented, maximum horizontal stress with an anticlockwise rotation of about 15° from the Otway Basin to the Gippsland Basin. A general increase in minimum horizontal stress magnitude from the Otway Basin towards the Gippsland Basin is also observed. The present-day state-of-stress has been interpreted as strike-slip in the South Australian (SA) Otway Basin, strike-slip trending towards reverse in the Victorian Otway Basin and borderline strike-slip/reverse in the Gippsland Basin. The present-day stress states and the orientation of the maximum horizontal stress are consistent with previously published earthquake focal mechanism solutions and the neotectonic record for the region. The consistency between measured present-day stress in the basement (from focal mechanism solutions) and the sedimentary basin cover (from petroleum well data) suggests a dominantly tectonic far-field control on the present-day stress distribution of southeast Australia. The rotation of the maximum horizontal stress and the increase in magnitude of the minimum horizontal stress from west to east across southeast Australia may be due to the relative proximity of the New Zealand segment of the plate boundary.

The Lake Keowee, South Carolina Earthquakes of February through July 1986

1987 ◽  
Vol 59 (2) ◽  
pp. 63-70 ◽  
Author(s):  
Steven D. Acree ◽  
Jill R. Acree ◽  
Pradeep Talwani
Keyword(s):  
South Carolina ◽  
Focal Mechanism ◽  
Horizontal Stress ◽  
Early Morning ◽  
Free Solution ◽  
Epicentral Area ◽  
Focal Mechanism Solutions ◽  
Duration Magnitude ◽  
First Motion ◽  
Maximum Horizontal Stress

Abstract In the early morning of 13 February 1986, an earthquake with a duration magnitude (MD) of 3.2 rumbled through northwestern South Carolina. The event was centered near Lake Keowee in Oconee County in a region of prior low level seismicity. Approximately eighty aftershocks with magnitudes ranging from −1.0 to 2.0 were recorded during the next six days. The locations of five aftershocks were accurately determined, utilizing data from portable seismographs deployed in the epicentral area. Depths of the two earthquakes with a location quality of B or better were between 3 and 4 km. First motion focal mechanism solutions for the mainshock suggest oblique slip along a plane striking northeast or northwest. The P axis was oriented northeast-southwest in support of the directions obtained from mechanisms of other local earthquakes and from direct measurements of the maximum horizontal stress in the regions. A second mainshock (MD = 2.8) occurred in the vicinity of Lake Keowee on 11 June 1986 and was followed by over sixty earthquakes during the next five weeks. Focal mechanism solutions from first motion data obtained for the mainshock resemble those of the 13 February event and suggest oblique slip along a northeast or northwest striking plane. Depths of the best located aftershocks were approximately 1 km. Two tests were applied to the data to assess the reliability of the depth estimates. These involve the determination that the plot of RMS travel time residual versus fixed solution depth exhibits a single, sharp RMS minimum at the depth obtained from a free solution (depth uniqueness) and that the final free solution depth is not dependent upon the choice of starting depth (depth stability). Free solution depths obtained for the majority of the better located aftershocks were found to be unique and stable at depths between 1 and 4 km. A northeast trending anomaly is prominent in the geophysical data for this area. This anomaly is interpreted to result from an abrupt, lateral change in lithology along a shallow, northeast striking plane. The earthquakes do not appear to be associated with this feature. Instead, these earthquakes appear to be associated with a shallow body and may represent slip along northeast or northwest striking joints. The proximity of these earthquakes to Lake Keowee suggests the possibility of reservoir triggering. No correlation between seismicity and reservoir level is evident prior to the February events. Rapid fluctuations in water level did precede the events in June and July, providing possible triggering mechanisms.

scholarly journals Focal mechanisms and the stress field in the aftershock area of the 2018 Hokkaido Eastern Iburi earthquake (MJMA = 6.7)

2021 ◽  
Vol 73 (1) ◽  
Author(s):  
Yuki Susukida ◽  
◽  
Kei Katsumata ◽  
Masayoshi Ichiyanagi ◽  
Mako Ohzono ◽  
...  
Keyword(s):  
Stress Field ◽  
Principal Stress ◽  
Focal Mechanism ◽  
P Wave ◽  
Japan Meteorological Agency ◽  
Inversion Method ◽  
Reverse Fault ◽  
Focal Mechanism Solutions ◽  
Fault Type ◽  
Aftershock Area

AbstractThe tectonic stress field was investigated in and around the aftershock area of the Hokkaido Eastern Iburi earthquake (MJMA = 6.7) occurred on 6 September 2018. We deployed 26 temporary seismic stations in the aftershock area for approximately 2 months and located 1785 aftershocks precisely. Among these aftershocks, 894 focal mechanism solutions were determined using the first-motion polarity of P wave from the temporary observation and the permanent seismic networks of Hokkaido University, Japan Meteorological Agency (JMA), and High Sensitivity Seismograph Network Japan (Hi-net). We found that (1) the reverse faulting and the strike-slip faulting are dominant in the aftershock area, (2) the average trend of P- and T-axes is 78° ± 33° and 352° ± 51°, respectively, and (3) the average plunge of P- and T-axes is 25° ± 16° and 44° ± 20°, respectively: the P-axis is close to be horizontal and the T-axis is more vertical than the average of the P-axes. We applied a stress inversion method to the focal mechanism solutions to estimate a stress field in the aftershock area. As a result, we found that the reverse fault type stress field is dominant in the aftershock area. An axis of the maximum principal stress (σ1) has the trend of 72° ± 7° and the dipping eastward of 19° ± 4° and an axis of the intermediate principal stress (σ2) has the trend of 131° ± 73° and the dipping southward of 10° ± 9°, indicating that both of σ1- and σ2-axes are close to be horizontal. An axis of the minimum principal stress (σ3) has the dipping westward of 67° ± 6° that is close to be vertical. The results strongly suggest that the reverse-fault-type stress field is predominant as an average over the aftershock area which is in the western boundary of the Hidaka Collision Zone. The average of the stress ratio R = (σ1 − σ2)/(σ1 − σ3) is 0.61 ± 0.13 in the whole aftershock area. Although not statistically significant, we suggest that R decreases systematically as the depth is getting deep, which is modeled by a quadratic polynomial of depth.

scholarly journals Re-examining the stress field of the broader southern Aegean subduction area using an updated focal mechanism database

2017 ◽  
Vol 47 (2) ◽  
pp. 563 ◽  
Author(s):  
Ch. Kkallas ◽  
C.B. Papazachos ◽  
E.M. Scordilis ◽  
B.N. Margaris
Keyword(s):  
Stress Field ◽  
Focal Mechanism ◽  
Fault Plane ◽  
Aegean Sea ◽  
Detailed Examination ◽  
Slip Direction ◽  
Focal Mechanism Solutions ◽  
Temporary Network ◽  
Final Stress ◽  
The Ideal

We have employed the data of EGELADOS temporary network (October 2005-April 2007) to determine 88 focal mechanism solutions from Southern Aegean Sea using the RAPIDINV algorithm (Cesca et al., 2010). The new focal mechanism solutions determined, complemented with the previously available ones for Southern Aegean Seα provide the basis for a detailed examination of the stress field, using the distribution of P and T axes. To obtain the stress field we applied the method of Gephart and Forsyth (1984), namely the grid search inversion approach of Gephart (1990a,b), which incorporates the P and T axes of selected focal mechanisms. For the inversion, the initial stress solutions were computed by the “average” kinematic P and T-axis approach of Papazachos and Kiratzi (1992). The stress-inversion allows choosing the "ideal" fault plane corresponding to the minimum misfit rotation about an axis of general orientation which is needed to match an observed fault plane/slip direction with one consistent with the final stress model.

scholarly journals Focal Mechanisms and the Stress Field in the Aftershock Area of the 2018 Hokkaido Eastern Iburi Earthquake (MJMA = 6.7)

2020 ◽  
Author(s):  
Yuki Susukida ◽  
Kei Katsumata ◽  
Masayoshi Ichiyanagi ◽  
Mako Ohzono ◽  
Hiroshi Aoyama ◽  
...  
Keyword(s):  
Stress Field ◽  
Principal Stress ◽  
Focal Mechanism ◽  
P Wave ◽  
Japan Meteorological Agency ◽  
Inversion Method ◽  
Reverse Fault ◽  
Focal Mechanism Solutions ◽  
Fault Type ◽  
Aftershock Area

Abstract The tectonic stress field was investigated in and around the aftershock area of the Hokkaido Eastern Iburi earthquake (MJMA = 6.7) occurred on 6 September 2018. We deployed 26 temporary seismic stations in the aftershock area for approximately 2 months and located 1785 aftershocks precisely. Among these aftershocks 818 focal mechanism solutions were determined using the first motion polarity of P wave from the temporary observation and the permanent seismic networks of Hokkaido University, Japan Meteorological Agency (JMA), and High Sensitivity Seismograph Network Japan (Hi-net). We found that (1) the reverse faulting and the strike-slip faulting are dominant in the aftershock area, (2) the average azimuths of P- and T-axes are N78° ± 33°E and N3° ± 52°W, respectively, and (3) the average dips of P- and T-axes are 25° ± 16° and 46° ± 20°, respectively: the P-axis is close to be horizontal and the T-axis is close to be vertical. We applied a stress inversion method to the focal mechanism solutions to estimate a stress field in the aftershock area. As a result, we found that the reverse fault type stress field is dominant in the aftershock area. An axis of the maximum principal stress (σ1) has the azimuth of N73° ± 8°E and the dipping eastward of 17° ± 6° and an axis of the medium principal stress (σ2) has the azimuth of N126° ± 91°E and the dipping southward of 16° ± 13°, indicating that both of σ1- and σ2-axes are close to be horizontal. An axis of the minimum principal stress (σ3) has the dipping westward of 64° ± 9° that is close to be vertical. The results strongly suggest that the reverse-fault-type stress field is predominant as an average over the aftershock area which is in the western boundary of the Hidaka Collision Zone. Although the average of the stress ratio is R = 0.6 ± 0.2 in the whole aftershock area, R decreases systematically as the depth is getting deep, which is modeled by a quadratic polynomial of depth.

scholarly journals Spatiotemporal Variations of Focal Mechanism Solutions and Stress Field of the 2019 Changning Ms 6.0 Earthquake Sequence

2022 ◽  
Vol 9 ◽  
Author(s):  
Zhiwei Zhang ◽  
Chuntao Liang ◽  
Feng Long ◽  
Min Zhao ◽  
Di Wang
Keyword(s):  
Stress Field ◽  
Focal Mechanism ◽  
Water Injection ◽  
Local Stress ◽  
Spatiotemporal Variations ◽  
Focal Mechanism Solutions ◽  
Principal Compressive Stress ◽  
Before And After ◽  
The Sichuan Basin

The June 17, 2019, MS 6.0 Changning earthquake is the largest recorded event in the Sichuan basin, spatiotemporal variations of stress field may shed light on the seismogenic mechanism of the earthquake. We determined the focal mechanism solutions (FMSs) of 124 earthquakes with MS ≥ 3.0 occurring in the Changning area from April 1, 2007, to February 29, 2020, and analyzed changes of FMSs and stress field before and after Changning earthquake. The Changning aftershocks were predominantly thrust fault earthquakes, followed by strike slip. The P-axis azimuths of the aftershock FMSs were oriented predominantly in the NEE direction, notably differing from the NWW-oriented P-axis azimuths of pre-earthquake FMSs; it shows the rotation of local stress field before and after the Changning earthquake, it is speculated that the change of stress field in Changning area may be caused by long-term water injection and salt mining activities. From the southeast to the northwest of the aftershock zone, the azimuths of principal compressive stress (S1) change from NEE to near-EW in both horizontal and vertical planes. Significant changes occurred in the FMS types and stress field of the aftershock zone following the Changning earthquake, the FMSs became diverse, the S1 azimuth of the Changning area changed from NWW to NEE, and then EW, the plunge and stress tensor variances increased, it reflects that the stress field of the Changning area adjusts continually with time.

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