Directional Statistics, Bayesian Methods of Earthquake Focal Mechanism Estimation, and Their Application to New Zealand Seismicity Data

Leibler Divergence ◽

Focal Mechanism Estimation

<p>A focal mechanism is a geometrical representation of fault slip during an earthquake. Reliable earthquake focal mechanism solutions are used to assess the tectonic characteristics of a region, and are required as inputs to the problem of estimating tectonic stress. We develop a new probabilistic (Bayesian) method for estimating the distribution of focal mechanism parameters based on seismic wave polarity data. Our approach has the advantage of enabling us to incorporate observational errors, particularly those arising from imperfectly known earthquake locations, allowing exploration of the entire parameter space, and leads to natural point estimates of focal mechanism parameters. We investigate the use of generalised Matrix Fisher distributions for parameterising focal mechanism uncertainties by minimising the Kullback-Leibler divergence. We present here the results of our method in two situations. We first consider the case in which the seismic velocity of the region of interest (described by a velocity model) is presumed to be precisely known, with application to seismic data from the Raukumara Peninsula, New Zealand. We then consider the case in which the velocity model is imperfectly known, with application to data from the Kawerau region, New Zealand. We find that our estimated focal mechanism solutions for the most part are consistent with all available polarity data, and correspond closely to solutions obtained using established methods. Further, the generalised Matrix Fisher distributions we examine provide a good fit to our Bayesian posterior PDF of the focal mechanism parameters, enabling the posterior PDF to be succinctly summarised by reporting the estimated parameters of the fitted distribution.</p>

A functional tool to explore the reliability of micro-earthquake focal mechanism solution for seismotectonic purposes

10.5194/se-2021-88 ◽

2021 ◽

Author(s):

Guido Maria Adinolfi ◽

Raffaella De Matteis ◽

Rita De Nardis ◽

Aldo Zollo

Keyword(s):

Focal Mechanism ◽

Fault Plane ◽

Focal Mechanisms ◽

Seismic Network ◽

Fault System ◽

Focal Mechanism Solution ◽

Fault Plane Solutions ◽

Stress Regime ◽

Earthquake Focal Mechanism

Abstract. Improving the knowledge of seismogenic faults requires the integration of geological, seismological, and geophysical information. Among several analyses, the definition of earthquake focal mechanisms plays an essential role in providing information about the geometry of individual faults and the stress regime acting in a region. Fault plane solutions can be retrieved by several techniques operating in specific magnitude ranges, both in the time and frequency domain and using different data. For earthquakes of low magnitude, the limited number of available data and their uncertainties can compromise the stability of fault plane solutions. In this work, we propose a useful methodology to evaluate how well a seismic network used to monitor natural and/or induced micro-seismicity estimates focal mechanisms as function of magnitude, location, and kinematics of seismic source and consequently their reliability in defining seismotectonic models. To study the consistency of focal mechanism solutions, we use a Bayesian approach that jointly inverts the P/S long-period spectral-level ratios and the P polarities to infer the fault-plane solutions. We applied this methodology, by computing synthetic data, to the local seismic network operated in the Campania-Lucania Apennines (Southern Italy) to monitor the complex normal fault system activated during the Ms 6.9, 1980 earthquake. We demonstrate that the method we propose can have a double purpose. It can be a valid tool to design or to test the performance of local seismic networks and more generally it can be used to assign an absolute uncertainty to focal mechanism solutions fundamental for seismotectonic studies.

PRESENT-DAY STATE-OF-STRESS OF SOUTHEAST AUSTRALIA

The APPEA Journal ◽

10.1071/aj05016 ◽

2006 ◽

Vol 46 (1) ◽

pp. 283 ◽

Cited By ~ 18

Author(s):

E. Nelson ◽

R. Hillis ◽

M. Sandiford ◽

S. Reynolds ◽

S. Mildren

Keyword(s):

Focal Mechanism ◽

Horizontal Stress ◽

Strike Slip ◽

Southeast Australia ◽

State Of Stress ◽

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.

Selective Manifestation of Sesmogenic Stress Field within the Mediterranean Belt (Based on Earthquake Focal Mechanism Solutions)

Journal of Volcanology and Seismology ◽

10.1134/s0742046317060069 ◽

2017 ◽

Vol 11 (6) ◽

pp. 447-461

Author(s):

Yu. M. Volfman ◽

E. Ya. Kolesnikova ◽

B. G. Pustovitenko ◽

V. K. Milyukov

Keyword(s):

Stress Field ◽

Focal Mechanism ◽

The Mediterranean

A functional tool to explore the reliability of micro-earthquake focal mechanism solutions for seismotectonic purposes

Solid Earth ◽

10.5194/se-13-65-2022 ◽

2022 ◽

Vol 13 (1) ◽

pp. 65-83

Author(s):

Guido Maria Adinolfi ◽

Raffaella De Matteis ◽

Rita de Nardis ◽

Aldo Zollo

Keyword(s):

Focal Mechanism ◽

Fault Plane ◽

Normal Fault ◽

Focal Mechanisms ◽

Seismic Network ◽

Fault System ◽

Fault Plane Solutions ◽

Stress Regime ◽

Earthquake Focal Mechanism

Abstract. Improving the knowledge of seismogenic faults requires the integration of geological, seismological, and geophysical information. Among several analyses, the definition of earthquake focal mechanisms plays an essential role in providing information about the geometry of individual faults and the stress regime acting in a region. Fault plane solutions can be retrieved by several techniques operating in specific magnitude ranges, both in the time and frequency domain and using different data. For earthquakes of low magnitude, the limited number of available data and their uncertainties can compromise the stability of fault plane solutions. In this work, we propose a useful methodology to evaluate how well a seismic network, used to monitor natural and/or induced micro-seismicity, estimates focal mechanisms as a function of magnitude, location, and kinematics of seismic source and consequently their reliability in defining seismotectonic models. To study the consistency of focal mechanism solutions, we use a Bayesian approach that jointly inverts the P/S long-period spectral-level ratios and the P polarities to infer the fault plane solutions. We applied this methodology, by computing synthetic data, to the local seismic network operating in the Campania–Lucania Apennines (southern Italy) aimed to monitor the complex normal fault system activated during the Ms 6.9, 1980 earthquake. We demonstrate that the method we propose is effective and can be adapted for other case studies with a double purpose. It can be a valid tool to design or to test the performance of local seismic networks, and more generally it can be used to assign an absolute uncertainty to focal mechanism solutions fundamental for seismotectonic studies.

Crustal strain measurements in Nevada

Bulletin of the Seismological Society of America ◽

10.1785/bssa0640041319 ◽

1974 ◽

Vol 64 (4) ◽

pp. 1319-1328

Author(s):

Keith Priestley

Keyword(s):

Focal Mechanism ◽

Great Basin ◽

Strain Rates ◽

Strain Accumulation ◽

Strain Measurements ◽

Spreading Rates ◽

Inelastic Processes

abstract Strain measurements at two sites in central Nevada, Round Mountain and Mina, indicate that, in this area of the Basin and Range, strain rates are less than 2 × 10−6 per year. These observations are in agreement with estimated spreading rates and geodetic measurements in the Great Basin. The general agreement between strain-meter observations at Round Mountain and nearby focal mechanism solutions suggests that we are observing strain accumulation in this area. The long-term strain at Mina is more variable, but generally agrees with earthquake focal mechanism solutions. The strain rate, in conjunction with the high seismicity of the Mina area, suggests that strain has already accumulated and is presently being released through inelastic processes.

Stress inversion of earthquake focal mechanism solutions from onshore and offshore Norway

Norsk Geologisk Tidsskrift ◽

10.1080/00291960051030545 ◽

2000 ◽

Vol 80 (4) ◽

pp. 235-250 ◽

Cited By ~ 35

Author(s):

Erik C. Hicks ◽

Hilmar Bungum ◽

Conrad D. Lindholm

Keyword(s):

Focal Mechanism ◽

Stress Inversion ◽

Earthquake Focal Mechanism

Tectonic stress orientations and magnitudes, and friction of faults, deduced from earthquake focal mechanism inversions over the Korean Peninsula

Geophysical Journal International ◽

10.1093/gji/ggy061 ◽

2018 ◽

Vol 213 (2) ◽

pp. 1360-1373 ◽

Cited By ~ 18

Author(s):

Inho Soh ◽

Chandong Chang ◽

Junhyung Lee ◽

Tae-Kyung Hong ◽

Eui-Seob Park

Keyword(s):

Focal Mechanism ◽

Korean Peninsula ◽

Tectonic Stress ◽

Stress Orientations

Fault Geometry and Mechanism of the Mw 5.7 Nakchu Earthquake in Tibet Inferred from InSAR Observations and Stress Measurements

Remote Sensing ◽

10.3390/rs13245142 ◽

2021 ◽

Vol 13 (24) ◽

pp. 5142

Author(s):

Yujiang Li ◽

Yongsheng Li ◽

Xingping Hu ◽

Haoqing Liu

Keyword(s):

Focal Mechanism ◽

Historical Earthquakes ◽

Tectonic Stress ◽

Indian Plate ◽

Coseismic Deformation ◽

Normal Faulting ◽

Eurasian Plate ◽

Seismogenic Fault ◽

Stress Measurements ◽

Focal Mechanism Solutions

Different types of focal mechanism solutions for the 19 March 2021 Mw 5.7 Nakchu earthquake, Tibet, limit our understanding of this earthquake’s seismogenic mechanism and geodynamic process. In this study, the coseismic deformation field was determined and the geometric parameters of the seismogenic fault were inverted via Interferometric Synthetic Aperture Radar (InSAR) processing of Sentinel-1 data. The inversion results show that the focal mechanism solutions of the Nakchu earthquake are 237°/69°/−70° (strike/dip/rake), indicating that the seismogenic fault is a NEE-trending, NW-dipping fault dominated by the normal faulting with minor sinistral strike-slip components. The regional tectonic stress field derived from the in-situ stress measurements shows that the orientation of maximum principal compressive stress around the epicenter of the Nakchu earthquake is NNE, subparallel to the fault strike, which controlled the dominant normal faulting. The occurrence of seven M ≥ 7.0 historical earthquakes since the M 7.0 Shenza earthquake in 1934 caused a stress increase of 1.16 × 105 Pa at the hypocenter, which significantly advanced the occurrence of the Nakchu earthquake. Based on a comprehensive analysis of stress fields and focal mechanisms of the Nakchu earthquake, we propose that the dominated normal faulting occurs to accommodate the NE-trending compression of the Indian Plate to the Eurasian Plate and the strong historical earthquakes hastened the process. These results provide a theoretical basis for understanding the geometry and mechanics of the seismogenic fault that produced the Nakchu earthquake.