دانلود رایگان مقاله انگلیسی شدت زلزله های قدیمی، بزرگی زلزله و اثرات دینامیکی خاک. زلزله 1750 کرواسی - الزویر 2018

abstract

A problem in the study of pre-instrumental earthquakes is how to reconstruct their parameters based on usually fragmentary evidence of seismic intensities, which reflect the combined effect of fault dynamics, of radiation of seismic waves, and of local amplification or attenuation of strong seismic motions. This problem is highlighted in the 1750 earthquake in Croatia, in the active compressional margin of NW Adriatic, an area with rarely known seismic history. Recent high-quality historical and archaeological data revealed that the 1750 earthquake was associated with high (up to VIII) seismic intensities, which were assigned to local amplification of strong motion generated by a magnitude 5 earthquake. This scenario points to a nearly aseismic plate boundary and to an unusually long meizoseismal zone for a small earthquake. On the contrary, in this study, the 1750 earthquake is associated with a segment of a major thrust and with a M > 6.0 earthquake which produced moderate accelerations. These results were based on a triple correlation between (1) a Finite Fault Model derived from elastic dislocation analysis of differential subsidence of submerged coastal notches, (2) a major composite thrust and (3) the distribution of areas of high seismic intensities. This result provides some input for the estimation of the seismic hazard/risk in the study area, indicates that the Adria-Eurasia collision front in NW Croatia is not essentially aseismic, and highlights the need to include soil dynamics effects in the study of palaeoseismic events.

7. Conclusions

The 1750 Croatia earthquake was associated with high (VII-VIII) intensities along a distance of >40 km (Fig. 4), and their interpretation is a matter of debate, because soil dynamics effects are taken into consideration.

A first scenario suggests that observed high intensities during this and other historical earthquakes indicate local amplification of seismic accelerations/intensities in small karstic valleys (see Fig. 2) and low magnitude seismic events (~M5.0) in the last 500 years; this points to an unusual, essentially aseismic plate collision front in Northern Adriatic.

An alternative, preferred scenario is that although local amplification effects are definitely expected, the observed high (VII-VIII) intensities along a distance of >40 km (Fig. 4) cannot be explained by a moderate magnitude earthquake, even if directivity effects are taken into consideration. This result is consistent with finite fault modeling of the 1750 earthquake on the basis of elastic dislocation analysis of differential submersion of coastal notches. Model fault correlates with the Vinodol-Bakar Thrust, the major tectonic structure in the area, perhaps the only one which can generate major earthquakes, and the distribution of the intensities of the 1750 event. This triple correlation of independent lines of evidence permits to define the characteristics/parameters of the 1750 Croatia earthquake, a M > 6 magnitude event which produced normal to moderate seismic intensities.