The research conducted on the 6th of February 2023 Mw7.8 Kahramanmaraş earthquake representsa comprehensive study aimed at understanding the distribution of seismic intensity in the affectedareas and developing a novel intensity calculation formula for Eastern-Southeastern Turkey. Thisseismic event, the most catastrophic in Turkey's last century, was initiated on the Narli splay faultand propagated bilaterally along the East Anatolian Fault (EAF). The rupture extended over asignificant seismic gap of the EAF and the Amanos Fault, affecting 11 provinces in Turkey's Southeastregion and bordering areas of Syria, resulting in a total rupture length exceeding 300 km and causingover 50,000 fatalities.The study evaluates seismic intensity distribution across seven cities: Hatay, Gaziantep,Kahramanmaraş, Adıyaman, Malatya, Osmaniye, and Şanlıurfa. An online intensity questionnairesurvey was distributed to educational institutions in these provinces. In October 2023, a Turkish-Japanese reconnaissance team collaborated with the National Education Directorate of the sevenprovinces to disseminate the questionnaire format and URL link to all public high schools, middleschools, and elementary schools, garnering responses from 14,739 participants. Geocoordinateinputs were accurately assigned using the ArcGIS survey123 system, contributing to the preliminarysurvey results which included damage observations.Microtremor observations were conducted in Hatay, Gaziantep, Kahramanmaraş, and Adıyamanusing the Kinkei seismic measuring device developed in Japan. The research involved single-pointmicrotremor measurements at 20 locations within the earthquake zone, fault-fracture zones,damaged residential areas, particularly near the AFAD seismic stations. Additionally, arraymicrotremor measurements were made at 31 AFAD station locations with strong motion records.The analysis of 39 microtremor measurements revealed preliminary results indicating a correlationbetween heavily damaged buildings and areas where the Vs30 values are less than 180 m/s. Thefinding suggests that areas with lower Vs30 values may be more susceptible to damage duringearthquakes. These observations, combined with the result of the online intensity questionnaire surveys and localsoil amplifications, are utilized to assess the correlation between microtremor amplification andseismic damage. The objective is to formulate a new intensity calculation formula tailored to theEastern-Southeastern part of Turkey. This research's findings are anticipated to offer significantcontributions to earthquake intensity assessment methodologies, particularly in regions with distinctgeological and seismic profiles. The collaboration between Turkish and Japanese experts adds aninternational dimension to the study, potentially leading to improved seismic risk assessment,preparedness strategies, and recovery measures on a broader scale in the future.
We conducted single-site and array observations of microtremors in order to revise the shallow subsurface structure of the Furukawa district, Miyagi, Japan, where severe residential damage was reported during the Great Eastern Japan Earthquake of 2011, off the Pacific coast of Tohoku. The phase velocities of Rayleigh waves are estimated from array observations at three sites, and S-wave velocity models are established. The spatial distribution of predominant periods is estimated for the surface layer, on the basis of the spectral ratio of horizontal and vertical components (H/V) of microtremors obtained from single-site observations. We then compared ground motion records from a dense seismometer network with results of microtremor observations, and revised a model of the shallow (~100 m) subsurface structure in the Furukawa district. The model implies that slower near-surface S-wave velocity and deeper basement are to be found in the southern and eastern areas. It was found that the damage in residential structures was concentrated in an area where the average value for the transfer functions in the frequency range of 2 to 4 Hz was large.
Characterized Green’s function method (CGFM), a new approach for estimating the response spectra of earthquake ground motion, has been proposed by Oji et al. (2012). The CGFM is based on the concept that the spatial average of estimated results is equal to a conventional attenuation model. The site‐specific deviations can be modeled by the source rupture effects, such as directivity pulses and radiation patterns, which are represented by the frequency‐dependent factors obtained from a superposition of simple characterized waveforms obeying the omega‐square model. In this article, we expand the CGFM to include nonlinear site response at a specific site. This response is calculated using the estimated time history of ground motion on the engineering basement from the response spectrum and the simulated phase waveform obtained by the original CGFM. The proposed CGFM is verified by comparing the estimated results with the records from the 1995 Kobe and the 2007 Chuetsu‐Oki earthquakes, Japan.
We propose a direct estimation of dampings in surface layers based on the normalized energy density (NED). The ratio of the NED, defined as the NED for the uppermost layer divided by the NED for the basement, correlates well with the total damping, |$t_S^*$|. We apply the relation between the NED ratio and the total damping to estimate the total damping at an actual site, Katagihara (KTG) site in Japan. The total damping at the KTG site is directly estimated as |$t_S^*=0.038$|. This value agrees well with the estimated values determined from a conventional method, incorporating the non-linear inversion scheme.
An earthquake of JMA magnitude 6.5 (foreshock) hit Kumamoto Prefecture, Japan, at 21:26 JST on April 14, 2016. Subsequently, an earthquake of JMA magnitude 7.3 (main shock) hit Kumamoto and Oita Prefectures at 1:25 JST on April 16, 2016. The two epicenters were located adjacent to central Mashiki Town, and both events caused significantly strong motions. The heavy damage including collapse of residential houses was concentrated in “Sandwich Area” between Prefectural Route 28 and Akitsu River. During the main shock, we have successfully observed strong motions at TMP03 in Sandwich Area. Simultaneously with installation of the seismograph at TMP03 on April 15, 2016, between the foreshock and the main shock, a microtremor measurement was taken. After the main shock, intermittent measurements of microtremor at TMP03 were also taken within December 6, 2016. As the result, recovery process of shear wave velocities of volcanic soil at TMP03 before/after the main shock was revealed by time history of peak frequencies of the microtremor H/V spectra. Using results of original PS logging tests at proximity site of TMP03 on July 28, 2016, the applicability for the shear wave velocities to TMP03 was then confirmed based on similarity between the theoretical and monitored H/V spectra.
We focus on a complex rupture process, namely, multi-event generation within about 50 seconds during the 2011 off the Pacific coast of Tohoku Earthquake (Mw 9.0). We perform a 2D dynamic rupture simulation in order to explain physically the rupture process along the cross-section passing through the hypocenter. Realistic velocity structures are introduced into the simulation model. The dynamic parameters are selected by referring to kinematic source inversion results. The first significant event is generated on the deeper side of the fault. The scattered waves, mainly from the free surface, generate a stick-slip around the hypocenter, and then a second significant event is triggered. The synthetic waveforms consist of two major wave groups that are consistent with the observed ground motions.
