[S-SS12] 地震活動とその物理

[SSS12-P15] Characteristics of seismicity before and after the 2023 M7.7 and M7.5 Turkey earthquakes, revealed by integrating physics-based and statistical approaches

*楠城 一嘉^1,2,3,4、熊澤 貴雄³、井筒 潤^5,1、堀 高峰^4,1、長尾 年恭^6,1、尾池 和夫¹ (1.静岡県立大学、2.静岡大学、3.統計数理研究所、4.海洋研究開発機構、5.中部大学、6.東海大学)

キーワード：地震活動、地震間相互作用、地殻変動、断層、統計手法、b値

On February 6, 2023, a devastating earthquake of magnitude (M) 7.7 struck the East Anatolian fault zone bounding the Arabian and Anatolian tectonic plates. This quake, which occurred near the city of Kahramanmaraş in Turkey, was followed about nine hours later by a M7.5 quake approximately 90 km to the north of the initial M7.7 quake. We investigated the characteristics of seismicity before and after these doublet quakes, integrating physics-based and statistical approaches based on currently-observable data. We first confirmed previously-reported seismicity transients (seismic activation and low Gutenberg-Richter b-values) starting approximately eight months before the doublet quakes (Kwiatek et al., 2023; Över et al., 2023), using statistical models: Epidemic-Type Aftershock Sequence (ETAS) and Bayesian b-value (e.g., Kumazawa et al., 2019). We then noted a similar result to that obtained for seismicity prior to the 2011 Tohoku megaquake (Nanjo et al., 2012) showing a correlation between the distribution of areas with low b-values and that of high-slip areas of the eventual quake. Conducting physics-based Coulomb and statistical b-value analyses, we next found that locations of the largest and second largest events after the doublet quakes were in relatively high-stress regions and became closer to failure, caused by these doublet quakes. Furthermore, analysis of the ETAS model showed that the post-doublet-quake sequence is currently active but is decaying with time. The duration of this sequence was evaluated to be 2.7-5.5 years, longer than the duration (1-2.5 years) previously proposed (Toda and Stein, 2024). This evaluation is important because almost 1.5 years have passed since the M7.7 quake (as of Oct. 2024) and because the result provides basic information that can possibly be used for seismic hazard assessment of Turkey.
This study was partially supported by the MEXT under The Second Earthquake and Volcano Hazards Observation and Research Program (Earthquake and Volcano Hazard Reduction Research) (K.Z.N., T.K., J.I, T.N.) and under STAR-E (Seismology TowArd Research innovation with data of Earthquake) Program Grant Number JPJ010217 (K.Z.N., T.K.), and by Collaboration Research Program of IDEAS, Chubu University Grant Number IDEAS202417 (I.J., T.N. K.Z.N).
The paper partially associated with the presentation was submitted to Geosciences.