Areas around Bhavnagar and Jamnagar in eastern and northern parts of Saurashtra respectively, are identified previously as prone to recurrent earthquake swarm activity. Sparse seismotectonic studies so far have not revealed any linkage with known faults in Bhavnagar area while no structures are known to occur in the area around Jamnagar. We carried out detailed tectono-geomorphic studies with contrasting geomorphic settings with a view to provide an insight into the swarm activity from a geomorphological perspective. The study is based on extensive field studies and quantitative geomorphic analysis of landscape and drainage. The area around Bhavnagar is divisible into two tectono-geomorphic domains – the E-W trending Sihor Fault zone located to the west of Bhavnagar (domain-I) and the terrain to its south which shows undulating landscape controlled by N–S trending structural trends (domain-II). The quadrant in the SW between these two domains consists of southward titled trappean hills which form source area for drainages flowing northward through Sihor Fault zone and those flowing eastward through domain-II. Late Quaternary, possibly Holocene tectonic activity along the Sihor Fault is indicated by the northward tilt of alluvial plain surface, knickpoint in rivers and small scale minor faults along the fault zone, prominent decrease in depth of fluvial incision away from the fault zone and youthful landscape indicated by drainage basin analysis. Domain-II comprises the largely erosional pediplain developed over trappean and Tertiary rocks to the south of Bhavnagar. The drainages show an early stage of landscape development due to ongoing tectonic activity. The area around Jamnagar is dominantly a peneplain formed over subhorizontal trappean lava flows. The peneplain is a manifestation of the prolonged period of non-erosion and deposition during the Cenozoic. The rivers show youthful landscape in the central part of the peneplain which includes, large knickpoints, rapids, anomalous river bends, steepening of channel gradient and large potholes. This ENE-WSW trending zone of anomalous fluvial geomorphic anomalies points to the existence of a fault or fold in the subsurface. The structure appears to be active as indicated by the denser cluster of earthquake swarm along this zone. We infer that the generation of earthquake swarm activity comprising low to moderate magnitude shocks is caused by the sheared rocks along the Sihor Fault near Bhavnagar and the ENE-WSW trending subsurface structure near Lalpur which provide avenues for downward percolation of rainwater to deeper levels causing loss the frictional resistance along the weak planes.

Saurashtra东部和北部分别位于Bhavnagar和Jamnagar周围的区域以前被确定为容易发生反复地震群活动。迄今为止，稀疏地震构造研究尚未发现与Bhavnagar地区已知断层有任何联系，而Jamnagar周围地区则未发现任何构造。我们进行了详细的构造-地貌研究，对比了地貌背景，以期从地貌角度洞悉群居活动。该研究基于广泛的现场研究以及景观和排水的定量地貌分析。Bhavnagar周围的区域可分为两个构造-地貌区域-位于Bhavnagar西部的EW趋势Sihor断层带（I域）和其南部的地形，显示受N–S趋势结构趋势控制的起伏地形（域） -II）。这两个域之间的西南象限由向南的斜方山丘组成，形成了向北流经Sihor断层带和向东流经II域的排水的源区。冲积平原表面向北倾斜，河流的拐点和沿断层带的小规模小断层，表明沿着锡霍尔断裂的第四纪晚期构造活动，可能是全新世构造活动，远离断层带和年轻景观的河流切入深度明显减少流域分析表明。域II包括在Bhavnagar南部的斜方岩和第三纪岩石上形成的，具侵蚀性的大平原。由于正在进行的构造活动，排水沟显示出景观发展的早期阶段。Jamnagar周围的地区主要是在水平以下的梯形熔岩流上形成的Peneplain。Peneplain是新生代期间长时间不侵蚀和沉积的一种表现。河流在平原区的中部表现出年轻的景观，包括大的拐点，急流，异常的河道，河道坡度陡峭和大坑洼。河流异常地貌异常的这种ENE-WSW趋势带指出地下存在断层或褶皱。该结构似乎是活跃的，如沿着该区域的密集的地震群簇所示。