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Potential seismic hazards in the Sumatran Fault Zone (SFZ) have been highlighted as a consequence of significant earthquakes (MW ≥ 6.5). Fault geometry might control the initiation and propagation of rupture, which develops the importance of fault segmentation on the SFZ. In the last two decades, SFZ segments have been proposed through geological observations of surface traces using fractal and structural discontinuity analysis and seismic using seismicity clustering. This study presents a new insight into segmenting the SFZ using b-value changes through the maximum likelihood analysis to represent the characterization of the fault. We mapped a spatial analysis of b-values using a catalog of 681 shallow earthquakes with a moment magnitude (MW) between MW3.0 and MW5.6 with a standard error σ M W of ± 0.21, estimated by applying the spectral analysis method. We get the average of b-value along the SFZ, which is quite low at 0.9 with a standard error σ ¯ b of ± 0.031. The lowest b-value (b = 0.74) was observed in northern Sumatra (S1), and the highest b-value (b = 1.39) was in central Sumatra (S5). We analyzed the pattern of b-values changes spatially toward seismicity distribution. Based on b-value changes, we obtained the SFZ divided into 15 segments which describe a pattern of heterogeneity of b-value in characterizing the faults. These results provide a new perspective in explaining potential areas of seismic hazard along the segment of SFZ. [ABSTRACT FROM AUTHOR]

The potential earthquake and tsunami hazard along the Sumatra subduction margin, especially around the coast of West Sumatra-Bengkulu, was investigated based on the availability of pre-seismic surface displacement data and shallow crustal earthquake catalogue data from 1907 to 2016. The pre-seismic surface displacement data is based on the displacement data prior to and corrected displacement data after major earthquakes. Using the results of our previous study on the local covariance function and the relationship of Correlation Dimension (DC) with the b-value of Gutenberg-Richter (GR) Law, we estimated the maximum horizontal crustal strain rate (SHmax) and DC around the study area. Least squares prediction based on horizontal displacement data using the local covariance function is used to estimate the displacement model in the entire gridding study area with a 10 km x 10 km size. Furthermore, DC is calculated based on the b-value using the maximum likelihood method based on the input of a constant number of earthquake samples, assuming the regional b-value of GR Law equals 1. Furthermore, the spatial correlation of SHmax and DC can define the area of possible earthquake hazard potential. The identification results are then linked with previous stress reconstruction results for seismic hazard study and analysis. Based on the finding, we then estimate the Seismic Hazard Function (SHF) and Tsunami Height simulation to estimate the possible hazard risk at several observation points. We suggest that the result of this study could be beneficial to understand better the potential seismic and tsunami hazard in the future, mainly to support mitigation purposes. [ABSTRACT FROM AUTHOR]

An earthquake seismicity parameter study has been conducted in the southern part of the Sumatra Subduction Zone (SSZ) for the period of 1919 to 2019 with a hypocentre depth of 120 km and magnitude of ≥4Mw. The researched area is divided into three segments, Bengkulu, Lampung, and Sunda segments, respectively. This study aims to evaluate the seismicity parameters in the form of a-value, b-value, fractal dimension, and probabilities of earthquake recurrence period. Frequency-magnitude correlation statistical approach introduced by Gutenberg-Richter was used to calculate the seismicity parameters based on catalogue data obtained from USGS. An a-value variation of 5.11±1.84 to 5.85±2.46 obtained indicates the most dominant seismic intensity. b-value of 0.69±0,.17 to 0.83±0.35 correlates with high-stress levels, the level of spatial heterogeneity on the SFZ, and the probabilities of bigger earthquakes in the future. The calculation of fractal dimension of 1.4±0.33 to 1.7±0.71 indicates an earthquake distribution pattern was caused by a single fracture zone along the southern part of SSZ. The fracture zone is located on the left and right sides of the southern part of SSZ, which may not have been connected. In addition, the calculation result of earthquake recurrence period with magnitude ≥6.5Mw indicates that there will be an 5 - 6 earthquake event in the Bengkulu segment, 2 - 3 event in the Lampung segment, and 1 - 2 event in the Sunda segment, while the probabilities of an earthquake with magnitude ≥7.5Mw along the southern part of SSZ is 1 - 2 times. [ABSTRACT FROM AUTHOR]

We analyse the seismicity pattern including b-value in the north Sumatra-Great Nicobar region from 1976 to 2004. The analysis suggests that there were a number of significant, intermediate and short-term precursors before the magnitude 7.6 earthquake of 2 November 2002. However, they were not found to be so prominent prior to the magnitude 9.0 earthquake of 26 December 2004 though downward migration of activity and a 50-day short-term quiescence was observed before the event. The various precursors identified include post-seismic and intermediate-term quiescence of 13 and 10 years respectively, between the 1976 (magnitude 6.3) and 2002 earthquakes with two years (1990-1991) of increase in background seismicity; renewed seismicity, downward migration of seismic activity and foreshocks in 2002, just before the mainshock. Spatial variation in b-value with time indicates precursory changes in the form of high b-value zone near the epicenter preceding the mainshocks of 2004 and 2002 and temporal rise in b-value in the epicentral area before the 2002 earthquake. [ABSTRACT FROM AUTHOR]