GNGTS 2022 - Atti del 40° Convegno Nazionale

GNGTS 2022 Sessione 2.1 231 KINEMATIC AND DEPTH CONTROL ON MAGNITUDE-FREQUENCY RELATIONS: A CASE STUDY FROM SOUTHERN CALIFORNIA A. Carducci 1,2 , A. Petruccelli 3 , Rita de Nardis 1,2 , A. De Santis 4 , G. Lavecchia 1,2 1 Department of Psychological, Territory and Health Sciences, University of Chieti-Pescara, Italy 2 CRUST-Interuniversity Center for 3D Seismotectonics with territorial applications 3 Former Swiss Seismological Service, ETH Zurich, now at Leithà Srl - Unipol Group 4 INGV-Istituto Nazionale di Geofisica e Vulcanologia, Roma, Italy Abstract. We analyze the relationship between the frequency-magnitude parameter (e.g., b -value from the Gutenberg-Richter law) and fault kinematics in Southern California (SC), introducing a new faulting style parameter, referred to as A λ . The value of this parameter strictly depends on stress ratio φ as a function of rakes λ, expressed by the equations: A λ gives the advantage of associating kinematics and stress ratios to focal mechanisms without applying a formal inversion procedure. A λ ranges can be distinguished as follows: 0 ≤ A λ <3 for normal faults; 1 ≤ A λ <2 for strike-slip faults; 2≤ A λ <3 for reverse faults. In this work, we first compile a high-resolution focal mechanism catalog (time range: 1981 - 2019, magnitude range: 0 - 7.3) by combining the coordinates of Southern California Seismic Network earthquakes by Hauksson et al. (2012) with the focal mechanisms dataset compiled by Yang et al. (2012). Subsequently, applying the A λ parameter, we kinematically classify the resulting ~56700 focal mechanisms and calculate the Magnitude of Completeness Mc distributions for well-distinguished kinematic classes. The dataset displays sufficient spatial resolution to allow b -value computations along depth for the defined classes. Finally, the linear relation b ( A λ ) = b λ – k λ A λ , analog to the one proposed by Wu et al . (2018) for the Taiwan area, is explored at different depth ranges within these distributions, respecting known rheological passages within the SC crust. We suggest that this equation is well suited to express the dependencies between b-value, kinematics, and depths. References Hauksson, E., Yang, W., Shearer, P.M., 2012: Waveform Relocated Earthquake Catalog for Southern California (1981 to June 2011) . Bull. Seismol. Soc. Am. 102 , 2239–2244. https://doi.org/10.1785/0120120010. Wu, Y.-M., Chen, S.K., Huang, T.-C., Huang, H.-H., Chao, W.-A., Koulakov, I., 2018: Relationship Between Earthquake b -Values and Crustal Stresses in a Young Orogenic Belt . Geophys. Res. Lett. 45 , 1832–1837. https://doi. org/10.1002/2017GL076694. Yang, W., Hauksson, E., Shearer, P.M., 2012: Refined earthquake focal mechanism catalog for southern California (1981 - 2010) , Supplementary. Bull. Seism. Soc. Am. 10 , 2011–2012.