The Region of Metlaoui Facing Seismic Hazards: Study and Cartographic Approach (South Atlas of Tunisia)

The region of Metlaoui (South Atlas of Tunisia) is listed as one of the major seismotectonic zones of the national territory. About 10 major seismic events with moderate magnitude have occurred from the beginning of last century. The event of 7/11/1989 (Ms = 4.4) was undoubtedly the most important. It caused very significant material damage estimated at 224,525,000 Tunisian Dinars. This study uses a mapping tool to define areas with relatively high degrees of hazard and vulnerability. It also seeks to understand the active fault of the seismic events recorded in this region.

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.

Tectonic Environments of Strong Earthquakes in the North China Region

The North China Seismic Region is not a typical intraplate seismic region. Not only does it show a pervasive neotectonic influence of global plate geodynamics, but it also displays an atypical seismic activity rate, especially for strong earthquakes, for a region far from plate boundaries. It is obvious that the seismicity is related to the active seismotectonics and geodynamics of the deforming interior of a continental plate. The features of the seismotectonic zones and the tectonic setting of magnitude 6.0 or greater earthquakes in the region are discussed here. We conclude that strong earthquakes occur mainly in places where NE-trending main and NW-trending auxiliary tectonic zones intersect. Three types of mechanisms are suggested which differ according to the characteristics of different seismotectonic zones and which relate to different shallow and deep structures. These observed types of strong earthquakes in North China may represent the main categories of continental intraplate seismicity.