A comprehensive Survey of the 26 January 2001 Earthquake(Mw7.7) in the State of Gujarat, India

在震中地区寻找与地震有关的地表断层，特别是沿着已知的活动断层。但我们没有发现任何可能从深层成因断层延伸出来的地表断层。通过挖沟发现，布达莫拉村北部的压力脊是由表层横向扩张引起的。建立了一个由8个台站组成的临时地震台网，监测余震活动。记录到的余震分布在10至35公里的深度范围内；即中下地壳。从这一观察结果可以推断，导致断层没有到达地表。余震集中在一个向南倾斜的平面上，这表明地震是由一个向南倾斜的逆断层引起的。在震中及其周围设置了14个GPS观测站，以探测震后地壳变形。在两个月的时间间隔后观察到几厘米的垂直位移。通过MSK烈度和问卷烈度调查确定不同建筑类型的损伤程度，RC和砌体建筑的损伤原因，地面破坏和生命线结构的模式，场地效应和建筑物的微震观测，估计了损伤分布。据估计等震线显示，震中位于巴肖的直径为50公里的地区最大震级为10级，距离震中210公里的艾哈迈达巴德地区最大震级为6级。死亡率为6.5%，最高的是巴肖县，最高的是布吉县，最高的是1.6%。这场人道主义灾难的原因主要与砖石民居的倒塌有关。在钢筋混凝土结构的情况下，发现软层效应和钢筋不足造成了破坏，而1956年甘地达姆安贾尔地震后建造的钢筋混凝土结构的质量和性能更好。

Search for a surface fault associated with the earthquake was made over an epicentral area, especially along known active faults. But we could not find any surface faults that might have extended from the causative fault at depth. We found by trenching that the pressure ridge discovered in the north of Budarmora village was caused by lateral spreading of surface layer. A temporary seismograph network consisting of 8 stations was installed to monitor the aftershock activity. Recorded aftershocks are distributed in a depth range of 10 to 35 km ; i. e., the mid-to lower crust. It is inferred from this observation that the causative fault did not reach the the surface. The aftershocks are concentrated on a southerly dipping plane, which suggests that the earthquake was caused by a reverse fault dipping southward. An array of 14 GPS stations was set in and around the epicentral area to detect a post-seismic crustal deformation. Vertical displacements of a few centimeters were observed after a time interval of two months.Damage distribution was estimated investigating damage levels of different building types as defined by MSK intensity and questionnaire intensity survey, cause of damage in RC and masonry buildings, pattern of ground failure and lifeline structures, micro-tremor observation of site effects and buildings. Estimated isoseismals indicate maximum MSK intensity 10 in an area with a diameter of 50km with its center at Bhachau, and decrease to intensity 6 in Ahmedabad which is 210km distant from the epicenter. Fatality ratio was 6.5 % and highest in Bhachau district and 1.6 % in Bhuj district. The cause of the humanitarian disaster was mostly related with the collapse of masonry dwellings. In the case of RC structures, soft story effects and insufficient strengthening bars were found to have caused damages, while RC structures built after the 1956 Anjar earthquake in Ghandhidam indicated better quality and performance.