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

在震中区，特别是沿沿着已知的活动断层，搜寻与地震有关的地表断层。但我们找不到任何可能从深层成因断层延伸出来的地表断层。我们通过探槽发现，在Budarmora村北部发现的压力脊是由表层的侧向扩展造成的。安装了一个由8个台站组成的临时地震仪网络，以监测余震活动。记录到的余震分布在10至35公里的深度范围内; i.例如，中下地壳从这一观察结果可以推断，造成这种情况的断层没有到达地表。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。在震中地区及其周围设置了一个由14个全球定位系统站组成的阵列，以检测地震后的地壳变形。在两个月的时间间隔后，观察到几厘米的垂直位移。损坏分布估计调查不同类型的建筑物的损坏水平，定义的MSK强度和问卷调查强度调查，在钢筋混凝土和砌体结构的损坏原因，地面故障和生命线结构的模式，场地效应和建筑物的微动观测。估计的等震线表明，在直径50公里的地区，最大的MSK强度为10度，其中心位于Bhachau，在距离震中210公里的阿赫梅达巴德降至6度。死亡率为6. 5%，最高的是巴乔县，1. 6%在布杰县。人道主义灾难的原因主要与砖石住宅倒塌有关。在钢筋混凝土结构的情况下，软层效应和不足的加强筋被发现造成损害，而钢筋混凝土结构建成后，1956年安加尔地震在Ghandhidam表明更好的质量和性能。

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.