مجله ژئوفیزیک ایران

مجله ژئوفیزیک ایران

Investigation of anisotropy before and after Sisakht february 17, 2021 earthquake (Mn 5.4) using two independent methods: shear wave splitting and ambient noise interferometry

مقالات آماده انتشار

نوع مقاله : مقاله پژوهشی‌

نویسندگان
Mohadeseh Mohamadzadeh 1
Ahmad Sadidkhouy 2
Ramin Movaghari 3
1 M.Sc., Institute of Geophysics, University of Tehran, Tehran, Iran
2 Associate Professor, Institute of Geophysics, University of Tehran, Tehran, Iran
3 Postdoctoral research fellow, Southern University of Science and Technology, Shenzhen, Guangdong, China
10.30499/ijg.2024.476972.1631
چکیده
This study investigates the anisotropic characteristics of seismic waves following the Sisakht
earthquake on February 17, 2021, in the southwest of Iran. Our analysis of the anisotropic behavior of the region was conducted using two methodologies, shear wave splitting analysis (SWS) and
ambient noise interferometry (ANI). These methods provided complementary insights into the
subsurface dynamics influenced by seismic activity. The analysis of shear wave splitting used
continuous seismic data from the Kolanja station, which included 237 aftershocks (earthquake that occurs after a larger seismic event) and 63 foreshocks (earthquake that occurs before a larger seismic event). This extensive dataset allows us to analyze seismic wave behavior before and after the
earthquake. According to calculations, there was a significant shift in the orientation of fast-polarized S waves, which shifted from 114.5° prior to the earthquake to 93.46° following the earthquake.
According to this shift, there may have been an alteration in subsurface material properties. This indicates that the earthquake may have impacted the alignment or stress distribution within the crust of the Earth. In addition, we have observed an increase in the time delay between the slow and fast-polarized S waves before and after the earthquake, with the delay increasing from 0.08±0.01 seconds before to 0.1±0.01 seconds after the earthquake. This change highlights modifications in wave propagation characteristics and suggests potential reconfiguration of subsurface structures due to seismic activity. There has been an apparent change in the direction of anisotropy as well, from NW-SE before the earthquake to NE-SW afterward, indicating that the stress fields or material alignments within the crust have been altered. In addition to shear wave splitting, we analyzed ambient noise data from ten seismological stations in the region. By retrieving empirical Green's functions (EGFs) between various station pairs, Anisotropic parameters were derived based on azimuthal variations of Rayleigh wave group velocities. According to the results, our findings of shear wave splitting were corroborated, with an overall anisotropy direction change of approximately 6 degrees across the study area correlating with previous findings. The consistency between the NW-SE direction of anisotropy identified through ambient noise interferometry and shear wave splitting results reinforces the reliability of these results. This study enhances our understanding of how seismic events influence anisotropic properties in the Earth's crust, contributing valuable insights into subsurface dynamics in seismically active regions.
 
کلیدواژه‌ها
Seismic anisotropy, shear wave splitting, ambient noise interferometry, sisakht earthquake

موضوعات

عنوان مقاله English

Investigation of anisotropy before and after Sisakht february 17, 2021 earthquake (Mn 5.4) using two independent methods: shear wave splitting and ambient noise interferometry

نویسندگان English

Mohadeseh Mohamadzadeh 1
Ahmad Sadidkhouy 2
Ramin Movaghari 3
1 M.Sc., Institute of Geophysics, University of Tehran, Tehran, Iran
2 Associate Professor, Institute of Geophysics, University of Tehran, Tehran, Iran
3 Postdoctoral research fellow, Southern University of Science and Technology, Shenzhen, Guangdong, China
چکیده English

This study investigates the anisotropic characteristics of seismic waves following the Sisakht
earthquake on February 17, 2021, in the southwest of Iran. Our analysis of the anisotropic behavior of the region was conducted using two methodologies, shear wave splitting analysis (SWS) and
ambient noise interferometry (ANI). These methods provided complementary insights into the
subsurface dynamics influenced by seismic activity. The analysis of shear wave splitting used
continuous seismic data from the Kolanja station, which included 237 aftershocks (earthquake that occurs after a larger seismic event) and 63 foreshocks (earthquake that occurs before a larger seismic event). This extensive dataset allows us to analyze seismic wave behavior before and after the
earthquake. According to calculations, there was a significant shift in the orientation of fast-polarized S waves, which shifted from 114.5° prior to the earthquake to 93.46° following the earthquake.
According to this shift, there may have been an alteration in subsurface material properties. This indicates that the earthquake may have impacted the alignment or stress distribution within the crust of the Earth. In addition, we have observed an increase in the time delay between the slow and fast-polarized S waves before and after the earthquake, with the delay increasing from 0.08±0.01 seconds before to 0.1±0.01 seconds after the earthquake. This change highlights modifications in wave propagation characteristics and suggests potential reconfiguration of subsurface structures due to seismic activity. There has been an apparent change in the direction of anisotropy as well, from NW-SE before the earthquake to NE-SW afterward, indicating that the stress fields or material alignments within the crust have been altered. In addition to shear wave splitting, we analyzed ambient noise data from ten seismological stations in the region. By retrieving empirical Green's functions (EGFs) between various station pairs, Anisotropic parameters were derived based on azimuthal variations of Rayleigh wave group velocities. According to the results, our findings of shear wave splitting were corroborated, with an overall anisotropy direction change of approximately 6 degrees across the study area correlating with previous findings. The consistency between the NW-SE direction of anisotropy identified through ambient noise interferometry and shear wave splitting results reinforces the reliability of these results. This study enhances our understanding of how seismic events influence anisotropic properties in the Earth's crust, contributing valuable insights into subsurface dynamics in seismically active regions.

کلیدواژه‌ها English

Seismic anisotropy, shear wave splitting, ambient noise interferometry, sisakht earthquake
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مجله ژئوفیزیک ایران

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انتشار آنلاین از 01 شهریور 1404