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

在震中地区，特别是沿着已知的活动断层，对与地震有关的地表断层进行了搜索。但我们没有发现任何表面断层可能是从深层的起因断层延伸而来的。通过挖沟发现，在布达莫拉村北部发现的压脊是由表层的横向扩展造成的。安装了由8个台站组成的临时地震仪台网，以监测余震活动。有记录的余震分布在10到35公里的深度范围内，即中到下地壳。从这一观测结果可以推断，起因断层并没有到达地表。余震集中在向南倾斜的平面上，表明地震是由一条向南倾斜的逆断层引起的。在震中及其周围设置了由14个GPS站组成的阵列，以探测震后地壳形变。每隔两个月观测几厘米的垂直位移，通过MSK烈度和问卷烈度调查确定不同建筑类型的破坏程度，调查钢筋混凝土和砖石建筑的破坏原因，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，以估计损伤分布。估计的等震线表明，在直径50公里、中心位于巴豪的区域，MSK最大强度为10级，而在距离震中210公里的艾哈迈达巴德，强度降至6级。病死率为6.5%，Bhachau区最高，布吉区1.6%。人道主义灾难的原因主要与砖混房屋的倒塌有关。就钢筋混凝土结构而言，软层效应和钢筋不足造成了破坏，而1956年甘地坝安贾尔地震后建造的钢筋混凝土结构显示出更好的质量和性能。

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.