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Seismic source characteristics in the Kachchh rift basin and Saurashtra horst tectonic blocks in the stable continental region (SCR) of western peninsular India are studied using the earthquake catalog data for the period 2006-2011 recorded by a 52-station broadband seismic network known as Gujarat State Network (GSNet) running by Institute of Seismological Research (ISR), Gujarat. These data are mainly the aftershock sequences of three mainshocks, the 2001 Bhuj earthquake ( M 7.7) in the Kachchh rift basin, and the 2007 and 2011 Talala earthquakes ( M ≥ 5.0) in the Saurashtra horst. Two important seismological parameters, the frequency-magnitude relation ( b-value) and the fractal correlation dimension ( D) of the hypocenters, are estimated. The b-value and the D maps indicate a difference in seismic characteristics of these two tectonic regions. The average b-value in Kachchh region is 1.2 ± 0.05 and that in the Saurashtra region 0.7 ± 0.04. The average D in Kachchh is 2.64 ± 0.01 and in Saurashtra 2.46 ± 0.01. The hypocenters in Kachchh rift basin cluster at a depth range 20-35 km and that in Saurashtra at 5-10 km. The b-value and D cross sections image the seismogenic structures that shed new light on seismotectonics of these two tectonic regions. The mainshock sources at depth are identified as lower b-value or stressed zones at the fault end. Crustal heterogeneities are well reflected in the maps as well as in the cross sections. We also find a positive correlation between b- and D-values in both the tectonic regions. [ABSTRACT FROM AUTHOR]

Current assumptions on the level of inter-dependency between the magnitudes of earthquakes and the magnitudes of their aftershocks vary significantly, ranging from assumed independence for models like epidemic type aftershock-sequence (ETAS) to assumed positive correlation, at least for the events leading up to the largest earthquakes, for models like accelerated moment release. Recently, a method was developed by Marsan and Lengline for model independent stochastic de-clustering (MISD) of a multidimensional Hawkes self-exciting process, or as is the case here, earthquake activity. After expanding the algorithm to allow for a spatially dependent background rate (henceforth SDMISD), repeated application of SDMISD to a global earthquake catalog allows for estimates with confidence bounds for the average magnitude of an aftershock conditioned upon the magnitude(s) of the earthquake(s) that caused the aftershock. 15 years of data on M 5.3 earthquakes from the global Centroid Moment Tensor earthquake catalog indicate that the magnitudes of aftershocks are dependent on the magnitudes of the earthquakes that cause them, and indeed, larger than average earthquakes are more likely to trigger larger than average aftershocks. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

From the mainshocks of 85 Taiwan earthquakes ( M > 5) and their aftershocks reported in the Earthquake Data Report by NEIC PDE catalogue, several correlations between mainshocks and their aftershocks are studied. Results show that the magnitude difference (Δ M) between the mainshock and the largest aftershock slightly increases with the mainshock magnitude ( M) and varies from 0.1 to 2.2, with two values of 0.3 and 0.9 having the largest numbers of events. The mean value of Δ M is 0.83 ± 0.46. The differences of occurrence time and epicenter between the mainshock and the largest aftershock do not clearly correlate to M as well as Δ M. For the whole data set, 36.5 and 77.7% of the largest aftershocks are located near their individual mainshocks within a distance of 10 and 40 km, respectively. The difference in occurrence time somewhat increases as the difference of epicenters increases. [ABSTRACT FROM AUTHOR]

A destructive earthquake (Mw 6.1) struck East Java, Indonesia, on 10 April 2021, resulting in at least 10 deaths and damage to over 3000 buildings. Preliminary hypocenter determinations indicate that it was located ~20 km south of Java, at a depth of ~60 km, suggesting that it likely occurred within the subducting oceanic slab beneath the Sunda Arc. In order to better understand the origins of this important event, we have undertaken non-linear hypocenter determination of the mainshock and its aftershocks through picking of P- and S-wave arrival times recorded by nearby BMKG seismic stations, followed by precise relative relocation using the double-difference method. We have also conducted source mechanism analysis to determine the type of fault slip, and obtained a rupture model of the mainshock by performing a finite fault inversion. Our results show that the mainshock was intra-slab, with an estimated depth of 58 km and was followed by, on average, deeper aftershocks that ranged in depth from 57 to 69 km. The source mechanism solution of selected aftershocks reveal that they rupture along a thrust fault oriented almost parallel to the trench, which is consistent with the mainshock source solution. The rupture modelling results indicate that the earthquake is characterised by a high stress-drop and compact rupture area, which together with its depth of nearly 60 km, may explain the relatively small number of aftershocks that were recorded. [Display omitted] • The recent destructive intra-slab earthquake in East Java had few aftershocks. • This may be due to high stress-drop, compact rupture area, and focal depth of 60 km. • Such moderate-sized earthquakes can be a significant source of seismic hazard. [ABSTRACT FROM AUTHOR]

The April 3, 2017 M W 6.5, Moiyabana (Botswana) earthquake occurred in the continental interior of the Nubian plate and in a seismogenic region previously considered as stable. Our objective is to combine several approaches (field and remote sensing investigations) in order to adopt a multidisciplinary strategy so as to enhance our understanding of earthquake occurrence in intraplate southern Africa. We analyse the mainshock and aftershocks sequence based on a local seismic network and local seismotectonic characteristics. The earthquake rupture geometry is constrained with more than 900 aftershocks recorded over a period of three months and from the InSAR analysis of Sentinel-1 images (ascending orbit). The mainshock (25.134 E, 22.565 S; depth 22 ± 3 km) was followed by more than 500 events of magnitude M ≥ 0.8 recorded in April 2017 including the largest aftershock (M W 4.6 on the April 5, 2017). Focal mechanism solutions of the mainshock and aftershocks display predominance of NW-SE trending and NE dipping normal faulting. Stress inversion of the focal mechanisms produced results that are compatible with a NE-SW extension under normal faulting regime. The InSAR study shows fringes (a pair of ascending images 2017-03-30 and 2017-04-11) with two lobes with 3.86 cm–5.15 cm coseismic slip on a NW-SE elongated and 40-km-long surface deformation consistent with the mainshock location and normal faulting mechanism. The modelling of surface deformation provides the earthquake rupture dimension at depth with ~50 cm maximum slip on a fault plane striking 315°, dipping 45°, −80° rake and with M o 3.68 × 1018 Nm. Although the seismic strain rate is of low level, the occurrence of the 2017 Moiyabana earthquake, followed by an aftershock sequence in the central Limpopo Mobile Belt classifies the intraplate region as an active plate interior. • A study of the 2017 Botswana aftershock sequence in a continental interior. • The fault geometry from aftershocks analysis, InSAR and tectonic geomorphology. • Understanding earthquake generation processes using near-field seismology. • Possible development of new rifting zones within Nubia continental domain. [ABSTRACT FROM AUTHOR]