HR: 1330h
AN: S42E-0213    [PDF]
TI: The 1897 Shillong earthquake, northeast India: A new perspective on its seismotectonics and earthquake history
AU: * Rajendran, C
EM: cp_r@vsnl.com
AF: Center for Earth Science Studies, Akkulam, Trivandrum, Ker 695031 India
AU: Rajendran, K
EM: kusala@vsnl.com
AF: Center for Earth Science Studies, Akkulam, Trivandrum, Ker 695031 India
AB: The 1897 Shillong earthquake, northeast India is considered to be one of the largest in modern history. Oldham's memoir on this event widely considered as a classic treatise opened new vistas in observational seismology; many questions on the associated faulting mechanisms however remain unresolved. While most previous studies have suggested that the earthquake originated on a gentle north-dipping thrust that is considered to be associated with the Himalayan tectonics, a recent geodetic model by Bilham and England (2001) invokes a steep, south-dipping reverse fault, close to the northern topographic edge of the Shillong Plateau. This model, derived mostly from extant triangulation records, deviates from the conventional understanding of the faulting mechanism of this earthquake. Here, we interpret the available database on seismotectonics of the region and coseismic deformation associated with the 1897 earthquake, together with independent geomorphologic observations, to further understand the nature of faulting. Our interpretation of the morphologic features and coseismic level changes in the Brahmaputra valley, well logs, Bouguer gravity and earthquake data are consistent with a major, steep south-dipping fault, but it spatially conforms to the extreme northern margin of the Shillong massif, which occasionally outcrops on the northern bank of the Brahmaputra River. Our analysis of historical, archaeological and geological data implies a possible 1000-year-interval between the 1897 earthquake and its predecessor and we identify the northern boundary fault (named here as the Brahmaputra fault) as historically more active among other potential faults in the region. The overall tectonic scenario also indicates the critical role of the Brahmaputra in the progressive denudation of the northern plateau margin compared to its southern part (Dauki fault) and its impact on the seismotectonic processes associated with plateau uplift.
DE: 7221 Paleoseismology
DE: 7230 Seismicity and seismotectonics
SC: Seismology [S]
MN: 2003 Fall Meeting