Moment tensor inversion of recent small to moderate sized earthquakes: implications for seismic hazard and active tectonics beneath the Sea of Marmara

SUMMARY We retrieve the moment tensors of 64 small to moderate sized events that occurred mostly beneath the Sea of Marmara using near-field data recorded at strong-motion and broad-band seismic stations. The near-field displacement records are inverted to their sources utilizing Kuge’s method where the best fit between the synthetic and observed seismograms is achieved through searching a centroid moment tensor (CMT) point in a grid scheme. We also analyse the stress fields acting in the eastern and western parts of the Sea of Marmara by inverting the P- and T-axes of the focal mechanisms obtained. Significant biases in the stress tensors are obtained. The nearly horizontal maximum compressive axis σ 1 in the western part is rotated 16 ◦ counter-clockwise compared with σ 1 in the eastern part. The σ 2-axis is close to vertical (shear tectonic regime) in the east and the plunge of σ 2-axis in the west is 36 ◦ (transpressive tectonic regime). Changes in the σ 3-axis are also observed, that is, it is close to horizontal in the east and dips 49 ◦ in the west. The spatial distribution of the focal mechanisms suggests that the stress field in the eastern part of the Sea of Marmara is homogenous compared with the western part, and we identify five distinct subsidiary faults. (1) a WNW‐ESE-striking, right-lateral strike-slip fault located a few kilometres SW of the Princes’ Islands, (2) a WSW‐ENE-striking, right-lateral strike-slip fault named the Yalova‐Hersek fault, (3) an E‐W-striking normal fault located onshore between

[1]  B. Delouis,et al.  Focal mechanism determination and identification of the fault plane of earthquakes using only one or two near-source seismic recordings , 1999 .

[2]  N. Kraeva,et al.  Source parameter determination of local earthquakes in Korea using moment tensor inversion of single station data , 1999 .

[3]  Tuncay Taymaz,et al.  High-resolution seismic profiling in the Sea of Marmara (northwest Turkey): Late Quaternary sedimentation and sea-level changes , 1995 .

[4]  S. Ergintav,et al.  Interseismic Strain Accumulation in the Marmara Sea Region , 2002 .

[5]  B. Delouis,et al.  Determination of the fault plane using a single near-field seismic station with a finite-dimension source model , 1999 .

[6]  E. M. Anderson.  The dynamics of faulting , 1905, Transactions of the Edinburgh Geological Society.

[7]  A. Barka,et al.  Heightened odds of large earthquakes near istanbul: An interaction-based probability calculation , 2000, Science.

[8]  K. Kohketsu.  The extended reflectivity method for synthetic near-field seismograms , 1985 .

[9]  A. Špičák,et al.  Delimitation of domains with uniform stress in the subducted Nazca plate , 2000 .

[10]  Douglas S. Dreger,et al.  Determination of source parameters at regional distances with three‐component sparse network data , 1993 .

[11]  K. Feigl,et al.  Coseismic and Postseismic Fault Slip for the 17 August 1999, M = 7.5, Izmit, Turkey Earthquake. , 2000, Science.

[12]  D. Legrand,et al.  Moment tensor analysis of near-field broadband waveforms observed at Aso Volcano, Japan , 2000 .

[13]  Aral I. Okay,et al.  Active faults and evolving strike-slip basins in the Marmara Sea, northwest Turkey: a multichannel seismic reflection study , 2000 .

[14]  T. Tsapanos,et al.  Depth distribution of stresses in the Hokkaido Wadati-Benioff zone as deduced by inversion of earthquake focal mechanisms , 2000 .

[15]  Alain Geiger,et al.  GPS‐derived strain rate field within the boundary zones of the Eurasian, African, and Arabian Plates , 2000 .

[16]  John W. Gephart,et al.  An improved method for determining the regional stress tensor using earthquake focal mechanism data: Application to the San Fernando Earthquake Sequence , 1984 .

[17]  Kerry E Sieh,et al.  The transfer of slip between two en echelon strike‐slip faults: A case study from the 1992 Landers earthquake, southern California , 1995 .

[18]  Robert W. King,et al.  Global Positioning System measurements of present‐day crustal movements in the Arabia‐Africa‐Eurasia plate collision zone , 1997 .

[19]  A. Hasegawa,et al.  Aftershock Activity of the 1999 İzmit, Turkey, Earthquake Revealed from Microearthquake Observations , 2002 .

[20]  P. L. Hancock,et al.  Brittle microtectonics: principles and practice , 1985 .

[21]  D. Wells,et al.  New empirical relationships among magnitude, rupture length, rupture width, rupture area, and surface displacement , 1994, Bulletin of the Seismological Society of America.

[22]  T. Wallace,et al.  The determination of source parameters for small earthquakes from a single, very broadband seismic station , 1991 .

[23]  T. Lay,et al.  Long‐period regional wave moment tensor inversion for earthquakes in the western United States , 1995 .

[24]  S. K. Singh,et al.  Source parameters of the Pinotepa Nacional, Mexico, earthquake of 27 March, 1996 (Mw = 5.4) estimated from near-field recordings of a single station , 1997 .

[25]  T. Rockwell,et al.  Paleoseismology of the Gazikoy-Saros segment of the North Anatolia fault, northwestern Turkey: Comparison of the historical and paleoseismic records, implications of regional seismic hazard, and models of earthquake recurrence , 2001 .

[26]  Mustafa Aktar,et al.  The seismotectonics of the Marmara region (Turkey): results from a microseismic experiment , 2000 .

[27]  James Jackson,et al.  Seismicity of the Sea of Marmara (Turkey) since 1500 , 2000 .

[28]  J. Tchalenko.  Similarities between Shear Zones of Different Magnitudes , 1970 .

[29]  H. Kahle,et al.  GPS and geologic estimates of the tectonic activity in the Marmara Sea region, NW Anatolia , 1997 .

[30]  Cem Gazioğlu,et al.  Morphologic features of the Marmara Sea from multi-beam data , 2002 .

[31]  Demitris Paradissis,et al.  Global Positioning System constraints on plate kinematics and dynamics in the eastern Mediterranean and Caucasus , 2000 .

[32]  Aral I. Okay,et al.  An active, deep marine strike‐slip basin along the North Anatolian fault in Turkey , 1999 .

[33]  Haluk Ozener,et al.  Estimates of Seismic Potential in the Marmara Sea Region from Block Models of Secular Deformation Constrained by Global Positioning System Measurements , 2002 .

[34]  A. Barka,et al.  Strike‐slip fault geometry in Turkey and its influence on earthquake activity , 1988 .

[35]  T. Lüdmann,et al.  The Sea of Marmara: a plate boundary sea in an escape tectonic regime , 1995 .

[36]  Douglas S. Dreger,et al.  Aftershocks of the 1952 Kern County, California, earthquake sequence , 1999 .

[37]  Anderson,et al.  Active faults in the Sea of Marmara, western Turkey, imaged by seismic reflection profiles , 1999 .

[38]  J. Gephart.  Principal stress directions and the ambiguity in fault plane identification from focal mechanisms , 1985 .

[39]  C. Imren.  The North Anatolian Fault within the Sea of Marmara: a new interpretation based on multi-channel seismic and multi-beam bathymetry data , 2001 .

[40]  Douglas S. Dreger,et al.  Source parameters of the Sierra Madre Earthquake from regional and local body waves , 1991 .

[41]  John W. Gephart,et al.  FMSI: a FORTRAN program for inverting fault/slickenside and earthquake focal mechanism data to obtain the regional stress tensor , 1990 .

[42]  M. Aktar,et al.  Regional moment tensor inversion for strong aftershocks of the August 17, 1999 Izmit Earthquake (Mw=7.4) , 2001 .

[43]  Yoshimori Honkura,et al.  Seismic activity triggered by the 1999 Izmit earthquake and its implications for the assessment of future seismic risk , 2001 .