A Revisit to Seismic Hazard at Uttarakhand

This paper presents the seismic hazard of the state of Uttarakhand in India, located at the foothills of the seismically active Himalayan mountain ranges. In the present study, an updated catalog of earthquakes has been prepared for Uttarakhand which was homogenized into a unified moment magnitude scale after declustering of the catalog to remove aftershocks and foreshocks. Various source zones were identified in the study area to account for local variability in seismicity characteristics. The seismicity parameters were estimated for each of these source zones, which are necessary inputs into seismic hazard estimation of a region. The seismic hazard evaluation of the region based on a state-of-the art PSHA study was performed using the classical Cornell–McGuire approach with different source models and attenuation relations. The most recent knowledge of seismic activity in the region was used to evaluate the hazard, incorporating uncertainty associated with different modeling parameters as well as spatial and temporal uncertainties. The PSHA was performed with currently available data and their best possible scientific interpretation using an appropriate instrument such as the logic tree to explicitly account for epistemic uncertainty by considering alternative models. The hazard maps were produced for horizontal ground motion at the bedrock level and an attempt was done to bring the hazard at surface level using appropriate amplification factors. The maximum PHA value at bedrock level for 10% Probability of exceedance (PE) in 50 years is 0.34g and same for 2% PE in 50 years is 0.54g.

Study of the seismicity temporal variation for the current seismic hazard evaluation in Val d'Agri, Italy

This study examines the temporal variation of the seismicity in the Val d'Agri (southern Italy) and adjacent areas, for the current seismic hazard evaluation. The temporal variation of the seismicity is expressed as time series of the number of earthquakes, b value of Gutenberg–Richter relationship or b value of the frequency–magnitude distribution and the seismic energy released in the form of logE2/3. The analysis was performed by means of a new research tool that includes visualizing techniques, which helps the interactive exploration and the interpretation of temporal variation changes. The obtained time series show a precursory seismicity pattern, characterized by low and high probability periods, which preceded earthquakes of magnitude M ≥ 4.0. The 75% of the examined cases were successfully correlated with a change in seismicity pattern. The average duration of the low and the high probability periods is 10.6 and 13.8 months respectively. These results indicate that the seismicity temporal variation monitoring in a given area and the recognition of the low and high probability periods can contribute to the evaluation, in regular monthly intervals, of current seismic hazard status.

Study of the seismicity temporal variation for the current seismic hazard evaluation in Val d'Agri, Italy

This study examines the temporal variation of the seismicity in the Val d'Agri (Southern Italy) and adjacent areas, for the current seismic hazard evaluation. The temporal variation of the seismicity is expressed as time series of the number of earthquakes, the b value of the frequency magnitude distribution of Gutenberg-Richter relationship and the seismic energy released in the form of log E2/3. The analysis was performed by the means of a new research tool that includes visualizing techniques, which helps the interactive exploration and the interpretation of temporal variation changes. The obtained time series show a precursory seismicity pattern, characterized by low and high, probability periods, which preceded earthquakes of magnitude M ≥ 4.0. 75% of the examined cases were successfully correlated and 25 of them resulted false. The average duration of the low and the high probability periods is 10.6 and 13.8 months long respectively. These results indicate that the seismicity temporal variation monitoring in given area and the recognition of the low and high probability periods, can contribute to the evaluation, in regular monthly intervals, of the current status seismic hazard.

Updated seismotectonic zoning scheme of Metropolitan France, with reference to geologic and seismotectonic data

This work presents the seismotectonic zoning scheme of Metropolitan France developed by the IRSN (French Institute for Radioprotection and Nuclear Safety) within the framework of its seismic hazard assessment activities. It is the outcome of many years of work following the publication of the “seismotectonic atlas” in 1993 [Grellet et al., 1993]. This scheme supports the assessment of seismic hazard by IRSN. It takes into account the most recent data concerning the deep and surface geology, as well as those related to seismotectonics and tectonic activity. It finally includes 67 surface seismotectonic zones (STZ), as well as a catalogue of 74 faults or structures (named hereafter “potential active faults”) for which indications of Neogene to Quaternary displacement can be inferred. The description of the zoning scheme comes along with an estimation of the uncertainty on the boundary location between adjacent STZ. We also qualitatively determine a “relevance order” for each limit, so as to illustrate their reliability to separate regions of different seismogenic potential. Also, we attributed to the faults an indication whose purpose is to reflect the recent character of their activity, and thus their seismotectonic potential. This assessment of uncertainties was undertaken to better integrate the zoning scheme in the general approach, which arises from recent studies, namely the propagation of the uncertainties in seismic hazard evaluation, whether deterministic or probabilistic.