Himalaya – A Present-Day Evaluation of Its Thousand-Year Seismic Slip Potential

Date: 4/26/2019

Time: 08:45 AM

Room: Pike

Seismic, geodetic and felt-intensity observations from the 2015 Mw=7.8 Gorkha earthquake provide a template for the interpretation of pre-1960 earthquakes in the Himalaya. Four Mw>7.0 earthquakes since 1800 show striking similarities to the Nepal event and, as in 2015, are each inferred to have incremented elastic strain tens of km short of the frontal thrusts. Since no nearby major earthquakes have followed historical earthquakes, the resulting accumulating reservoir of elastic strain (invisible to geodesy once emplaced), is apparently impotent at nucleating spontaneous up-dip or along-strike contiguous ruptures. If this is a universal feature of M<8 Himalayan earthquakes it is obviously good news for the Kathmandu region where concerns have been expressed about the destiny and future evolution of the 2015 co-seismic strain-field. However, this latent strain, and reservoirs of relict strain energy elsewhere in the Himalaya, cannot persist indefinitely and are destined to be liberated in future great earthquakes. The ≥10 m of slip inferred for some paleoseismic surface ruptures may in large part be attributable to these Mw>8.5 earthquakes being fueled by inherited latent up-dip strain. The past 1000 years of earthquakes within 15 Himalayan segments between Kashmir and Assam are evaluated in the context of these new insights. In some places the current slip potential exceeds 10 m, and depending whether contiguous segments rupture individually or in parallel, a hierarchy of pending 8.0<Mw<8.7 scenario earthquakes can be envisaged. Two of these scenarios are for Mw=8.7 earthquakes. Alternatively, partial rupture of these regions could nucleate as many as seven Mw≥8.4 earthquakes. The current convergence rate is sufficient to generate a great (Mw=8) earthquake in every 180-km-long segment of the Himalaya once per century, i.e. one somewhere roughly every decade. History records just two great earthquakes in the past five centuries, signifying that the rupture of the Himalaya in one or more of these scenario ruptures must be considered overdue.

Presenting Author: Roger Bilham

Authors