Paleoearthquakes, The Law Of Strong Earthquake Recurrence And Potential Sites For The Occurrence Of Future Strong Earthquakes In The Hetao Fault-depression Zone

The theme of this thesis is selected as "Paleoearthquakes, the law of strong earthquake recurrence and potential sites for the occurrence of future strong earthquakes in the Hetao fault-depression zone" because of the following reasons: (1) .It is urgently needed to predict potential sites for the occurrence of future strong earthquakes in the Hetao fault-depression zone. (2) In the case of that parameters of models are difficult to be acquired or their uncertainties are very large, it is quite significant to research the law of strong earthquake recurrence in the Hetao fault-depression zone, to seek a suitable probability distribution model for the recurrence intervals of strong earthquakes, and to calculate the probability of occurrence of future strong earthquakes to predict the potential sites for the occurrence of future strong earthquakes on the basis of catalog of paleoearthquakes for each specific segment. (3) Based on the previous studies and with the support of the 973-ITEM, it is necessary and feasible to research further the active faults and paleoearthquakes in the Hetao fault-depression zone, and then the catalog of paleoearthquakes for each fault-segment can be compiled for probability distribution modeling.The study contents and the used technique of this work are summarized below.(1) Made data Collection and interpretation for all piedmont faults in the Hetao fault -depression zone and field geological reconnaissance in the whole region in order to investigate the geological background of occurrence of strong earthquakes and to select suitable locations for research on active faults or paleoearthquakes.(2) Surveyed the height distribution and collected dating-samples of all tectonic geomorphic planes in the segment eastern to Wublangkou of the Serteng piedmont fault and in the Wulashan piedmont fault to study the age and displacement distribution of each geomorphic plane, kinematics character and segmentation of these faults.(3) Selected carefully three sites, northwest of Hongmin village, west of Wulanhudong village in the Serteng piedmont fault and north of Hayehutong village in the Wulashan piedmont fault, for excavating big trenches to study paleoearthquakes in detail.(4) Lucubrated characteristics of strong earthquake recurrence and sought out the most suitable probability distribution model for the recurrence intervals of strong earthquakes according to the process of constructing Model of Northwest Beijing on the basis of the catalog of paleoearthquakes for some specific segments acquired by analyzing and summarizing systemically.(5) Analyzed interaction among segments or faults by means of moving window test.(6) Calculated the probabilities of occurrence of future strong earthquakes with the BPT model and the constructed probability-distribution model, named as Hetao model. Through comprehensive analyses, the potential sites for the occurrence of future strong earthquakes in the Hetao fault-depression zone are predicted.This work has obtained the following insights.(1) There are 4 specific active segments in the Serteng piedmont fault: Wujiahe segment, Wujumengkou-Dongfengcun segment, Dashetai segment and Wulanhudong segment. The average vertical slip rates are 0.22mm/a for the Dashetai segment and 0.20mm/a for the Wulanhudong segment since 29.46ka B.P. and 0.08mm/a for the Dashetai segment and0.11 mm/a for the Wulanhudong segment since 18.03ka B.P..(2) Along the Serteng piedmont fault, on the Dashetai segment there are 4 paleoseismic events since about 32ka B.P. which occurred orderly at 31690+1770 and 2300011320, 154201870, 7440l440a B.P. and their vertical displacements are 2.6 and 1.6, 2.2, 1.4m, respectively. This catalog is found to be a complete paleoseismic activity history. On the Wulanhudong segment there are 4 paleoseismic events since about 25ka B.P. which occurred orderly at 3169011770 and 2300011320, 154201870, 7440i440a B.P., and their vertical displacements are 2.6 and 1.6, 2.2, 1.4m, respectively. This catalog is found to...