85.12 FOCMEC: FOCal MEChanism determinations

Snoke, J. Arthur

doi:10.1016/s0074-6142(03)80291-7

Cited by 185 publications

(109 citation statements)

References 3 publications

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“…Focal plane solutions for the Cleburne earthquakes were calculated using the program FOCMEC (Snoke, 2009) which calculates the range of possible double-couple earthquake focal mechanisms consistent with P, SV, or SH polarities and/or amplitude ratios (SV=P, SH=P, SV=SH) (Kisslinger, 1980). FOCMEC was developed for local to regional events for which determining moment tensors from waveform modeling may be difficult.…”

Section: Focal Mechanismsmentioning

confidence: 99%

See 1 more Smart Citation

Analysis of the Cleburne, Texas, Earthquake Sequence from June 2009 to June 2010

Justinic¹,

Stump²,

Hayward³

et al. 2013

Bulletin of the Seismological Society of America

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On 9 June 2009, an M bLg 2.8 earthquake shook Cleburne, Texas, a community not known to have previously experienced earthquakes. Over 50 small earthquakes followed by the end of December 2009. A temporary network of four and then five IRIS-Passcal broadband systems was deployed from June 2009 to June 2010, recording data that were used to locate 38 events with the most confident P-and S-arrival picks. Event locations were distributed along a 2 km long north-northeast trend. The location centroid was at 32.298°N, 97.372°W and at 3.6 km depth. This location is approximately 1.3 km from a saltwater disposal well that began injection in October 2007 and 3.2 km away from a second injection well that was active from September 2005 to late July 2009. Focal mechanisms estimated for the best-recorded events suggest a north-northeast-south-southwest-trending normal fault with a dip of ∼50°and a component of oblique motion (rake of ∼ − 80°). This average solution is generally consistent with the north-northeast-trending extensional faults that are prevalent across parts of Texas, Oklahoma, Louisiana, and Arkansas. Stress drops calculated from P and S spectra for seven different events ranged from 3.9 to 90 bars, with most estimates between 40 and 50 bars, typical values for intraplate earthquakes. Because there were no known previous earthquakes, and the located events were close to the two injection wells and near the injection depth, the possibility exists that earthquakes may be related to fluid injection.Online Material: Tables of absolute and relative earthquake locations and a figure summarizing focal mechanism solutions.

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Section: Focal Mechanismsmentioning

confidence: 99%

“…The SH=P ratio was used because the SV peaks and troughs were harder to identify. Snoke (2009) notes that any amplitude ratio can be calculated from one of the other two, because they are dependent on one another.…”

Section: Focal Mechanismsmentioning

confidence: 99%

Analysis of the Cleburne, Texas, Earthquake Sequence from June 2009 to June 2010

Justinic¹,

Stump²,

Hayward³

et al. 2013

Bulletin of the Seismological Society of America

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“…The fault plane solutions are obtained by applying FOCMEC program (Snoke, 2000). The result shows that strike-slip faulting events predominate in the northern part of Yellow Sea and inland area of North Korea.…”

Section: Resultsmentioning

confidence: 99%

“…This study used the FOCMEC (FoCal MEChanism determination) program (Snoke, 2000(Snoke, , 2003, excuting the grid search not only for the trend and plunge of B axis (vertical to main compressional P axis and main dilatational T axis) in the range of 0 . The best fit nodal surface which satisfies both the polarity of the first P motion and SH/P amplitude ratio was determined.…”

Section: Fault Plane Solutionmentioning

confidence: 99%

Fault Plane Solutions of the Recent Earthquakes in the Northern Part of the Korean Peninsula

Lee¹,

Kyung²,

Cheol³

2014

Journal of the Korean earth science society

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was studied for the earthquakes that occurred from November, 2008 to May, 2013. The analysis was based on the data collected from seismic networks in Korea and China. Fault plane solutions were obtained from P and SH wave polarities and SH/P amplitude ratioes. Most earthquakes exhibited predominantly strike-slip fault characteristics with NNE-SSW or WNW-ESE nodal planes. The P-axes trends are mainly NE-SW or ENE-WSW direction in the northern part of the Yellow Sea and inland area of North Korea except some areas in the Hwanghae province. Fault plane solutions and main axis of stress field in the study region were similar to those observed in the southern part of the Korean Peninsula.

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“…We determined the individual focal mechanisms for two events by using both P-wave first motion polarities and S/P amplitude ratio (SNOKE, 2003) as done by many authors (i.e., MOHAMED et al, 2001;KANG and BAAG, 2004;KANG and SHIN, 2006;PLENEFISCH and KLINGE, 2003;BADAWY et al, 2009;RITTER et al, 2009). Unfortunately, it was not possible to obtain well-constrained fault plane solutions for all the events because in many cases the azimuthal distribution of the DEU-GFZ stations was inadequate.…”

Section: Focal Mechanisms and Stress Tensor Inversionmentioning

confidence: 99%

An Assessment of the Seismicity of the Bursa Region from a Temporary Seismic Network

Gök

Polat

2011

Pure Appl. Geophys.

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A temporary earthquake station network of 11 seismological recorders was operated in the Bursa region, south of the Marmara Sea in the northwest of Turkey, which is located at the southern strand of the North Anatolian Fault Zone (NAFZ). We located 384 earthquakes out of a total of 582 recorded events that span the study area between 28.50-30.00°E longitudes and 39.75-40.75°N latitudes. The depth of most events was found to be less than 29 km, and the magnitude interval ranges were between 0.3 B M L B 5.4, with RMS less than or equal to 0.2. Seismic activities were concentrated southeast of Uludag Mountain (UM), in the Kestel-Igdir area and along the Gemlik Fault (GF). In the study, we computed 10 focal mechanisms from temporary and permanents networks. The predominant feature of the computed focal mechanisms is the relatively widespread near horizontal northwest-southeast (NW-SE) T-axis orientation. These fault planes have been used to obtain the orientation and shape factor (R, magnitude stress ratio) of the principal stress tensors (r 1 , r 2 , r 3 ). The resulting stress tensors reveal r 1 closer to the vertical (oriented NE-SW) and r 2 , r 3 horizontal with R = 0.5. These results confirm that Bursa and its vicinity could be defined by an extensional regime showing a primarily normal to oblique-slip motion character. It differs from what might be expected from the stress tensor inversion for the NAFZ. Different fault patterns related to structural heterogeneity from the north to the south in the study area caused a change in the stress regime from strike-slip to normal faulting.

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85.12 FOCMEC: FOCal MEChanism determinations

Cited by 185 publications

References 3 publications

Analysis of the Cleburne, Texas, Earthquake Sequence from June 2009 to June 2010

Analysis of the Cleburne, Texas, Earthquake Sequence from June 2009 to June 2010

Fault Plane Solutions of the Recent Earthquakes in the Northern Part of the Korean Peninsula

An Assessment of the Seismicity of the Bursa Region from a Temporary Seismic Network

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