Absence of Near-Trench Early Triggering during the 2012 Mw 7.2 Indian Ocean Strike-Slip Earthquake: Evidence from One-Day Aftershocks

Dynamic earthquake triggering is a widely accepted mechanism of earthquake interaction, which plays a vital role in seismic hazard estimation, although its efficacy at regional distances is under debate. The 2012 Mw 7.2 Indian Ocean event is one of the first reported events to produce dynamic stress triggering at regional distances using backprojection (BP) techniques. Alternatively, the coherent radiators in BP images can be interpreted as localized water reverberation phases. We present further evidence against near-trench triggering during this event. We collected 24 hr seismic recordings of two nearby stations located near the trench. We adopted a waveform denoising algorithm and detected 125 aftershocks using two regional seismic stations with a minimum magnitude of ML∼2.7 and completeness magnitude of ML∼3.6, whereas none of these aftershocks occurred near the trench. The absence of immediate (within one day) aftershocks near the trench suggest the absence of dynamic triggering during the offshore mainshock.

Geodetic Model of the March 2021 Thessaly Seismic Sequence Inferred from Seismological and InSAR Data

In this work, we propose a geodetic model for the March 2021 Thessaly seismic sequence (TSS). We used the interferometric synthetic aperture radar (InSAR) technique and exploited a dataset of Sentinel-1 images to successfully detect the surface deformation caused by three major events of the sequence and constrain their kinematics, further strengthened by seismic data analysis. Our geodetic inversions are consistent with the activation of distinct blind faults previously unknown in this region: three belonging to the NE-dipping normal fault associated with the Mw 6.3 and Mw 6.0 events, and one belonging to the SW-dipping normal fault associated with the Mw 5.6, the last TSS major event. We performed a Coulomb stress transfer analysis and a 1D pore pressure diffusivity modeling to investigate the space–time evolution of the sequence; our results indicate that the seismic sequence developed in a sort of domino effect. The combination of the lack of historical records of large earthquakes in this area and the absence of mapped surface features produced by past faulting make seismic hazard estimation difficult for this area: InSAR data analysis and modeling have proven to be an extremely useful tool in helping to constrain the rupture characteristics.

Earthquake-induced liquefaction in the coastal zone, Case of Martil city, Morocco

According to historical documents and Moroccan earthquakes catalogs, the coastal zone has suffered in the past from several earthquakes. Understanding how sedimentary basins respond to seismic-wave energy generated by earthquake events is a significant concern for seismic-hazard estimation and risk analysis. The main goal of this study is to determine the distribution of the natural frequency value (F), the amplification factor value (A), and the soil vulnerability index (Kg) were carried out as an indicator for liquefaction potential sites in the Martil city based on the microtremor measurements. Liquefaction assessment was done at 96 stations using the HVSR approach provided by Nakamura (1989). According to the analysis results, the predominant frequency values range from about 0.31 to 5.63 Hz, and the amplification factor values range from 3 to 15. Based on these parameters, the vulnerability index Kg is determined, which can be used as a parameter in calculating the liquefaction potential of an area. This study shows supporting evidence for the first time that the HVSR of microtremors can be an excellent alternative indicator for an area's potential for liquefaction.

ANALISIS PENDUGAAN BAHAYA KEGEMPAAN DI BATUAN DASAR UNTUK WILAYAH LAMPUNG MENGGUNAKAN METODE PSHA

Analysis of seismic hazard estimation is one method for estimating the effect of earthquakes. The purpose of this study was to determine the maximum value of ground acceleration in bedrock or PGA values for the Lampung Province region. This analysis of seismic hazard estimation is carried out by a probabilistic seismic hazard analysis (PSHA) method. In the process of estimating the influence of earthquakes, the PSHA method principally uses 3 types of earthquake sources, namely the source of background earthquakes, subduction earthquakes (earthquake subduction) and fault earthquakes (faut). The calculation of the estimated seismic hazard value is carried out using the 2007 USGS PSHA program. The distribution of seismic hazard values for the Lampung Province region on bedrock with a 500-year return period or a 10% probability on the PGA condition (T = 0) is 0.1 g to 1, 3 g and a 2500 year return period or a probability of 2% in the PGA condition (T = 0) is 0.1 g to 1.3 g.

Seismotectonics of Malatya Fault, Eastern Turkey

Turkey is located in a seismically active region with a complex tectonic history. In order to perform seismic risk assessment precisely, major fault zones (North Anatolian Fault Zone and East Anatolian Fault Zone) that are well defined are monitored continuously. It is a widely known fact that intraplate settings, such as Anatolian Plate, in which devastating earthquakes may occur, need to be observed densely. In this study, we investigate the seismotectonics of Malatya Fault within the Malatya Ovacık Fault Zone (MOFZ), which is one of the major agents responsible for internal deformation acting on Anatolian Plate. Recent geological and paleoseismological studies underline the necessity of comprehending the seismicity and latency of a major earthquake in this fault zone.We applied traditional techniques to investigate data of such a region. Earthquakes that occured in the vicinity of Malatya Fault between the years 2011 and mid-2019 are employed in a detailed analysis. The results of this study are constrained by the distribution of sensor networks in the region, yet allowing to define an active structure which is not included in the active fault map of Turkey, therefore, making a significant contribution to seismic hazard estimation.

MACROSEISMICITY AND GEOLOGICAL EFFECTS OF THE WENCHUAN EARTHQUAKE (MS 8.0R - 12 MAY 2008), SICHUAN, CHINA: MACRO-DISTRIBUTION AND COMPARISON OF EMS1998 AND ESI2007 INTENSITIES

The Wenchuan earthquake of the 12th of May 2008, in Sichuan county of China can be classified as a large scale event based on the tectonic structures that triggered the earthquake and the effects caused on the human, structural and natural environment. The aim of this paper is to present the geotectonic and seismotectonic regime of the earthquake affected region based on field data along the seismic fault zone and an attempt is made towards the: (i) estimation of the intensity values according to EMS1998 (European Microseismic Scale, 1998) and ESI2007 (Environmental Seismic Intensity Scale, 2007) and the determination of their geographical distribution in a macroscale, (ii) interpretation of the intensity values data and their distribution according to the seismotectonic, geodynamic and geotechnical regime, and (iii) conduction of a comparative evaluation review on the application of both EMS1998 and ESI2007. The application of both EMS1998 and ESI2007 and the comparative evaluation of the results indicate that the estimated values of EMS1998 and ESI2007 were almost in agreement, despite the fact that the geographical locations of assessment data were different suggesting that the application and use of both scales appears to represent a useful and reliable tool for seismic hazard estimation.