Deformation of slopes damaged during the 2015 Nepal earthquake sequence

Abstract:

The 2015 Nepal Earthquake Sequence (EQS; the Gorkha EQ (_eqG), M_w 7.8 [25/04/15]; the Kodari EQ (_eqK), M_w 6.7 [26/05/15]; and Dolakha EQ (_eqD), M_w 7.3 [12/05/15], plus associated aftershocks) triggered widespread landsliding, strongly evident in satellite imagery. In addition to the observed failures, pervasive ground cracking has been widely reported in Nepal. This is indicative of hillslope ‘damage’ (weakening) and, hence, the onset of shear surface development in as-yet unfailed slopes  – a phenomenon previously observed in areas subjected to high-magnitude earthquake ground shaking and subsequent ongoing landsliding. Recent work on the efficacy of earthquakes in triggering landslides has proposed that the occurrence of failures is a function of damage accumulated in the slope.

We present a unique field monitoring dataset on continuing slope deformation from hillslopes damaged during the 2015 Nepal EQS, in response to precipitation and continuing seismicity. Our study site is the Upper Bhote Koshi (UBK), with sites chosen from a chronology of landslide inventories captured from remotely sensed imagery since the Gorkha earthquake. Instruments were deployed during the monsoon on new and pre-existing landslides, and across cracked ground to monitoring precipitation inputs, slope-scale (micro-)seismicity, and slope displacements. Using our dataset, we draw preliminary conclusions on how the spatially-variable legacy of damage accumulated during high-magnitude earthquake-induced ground shaking events is manifest in patterns, rates and styles of post-seismic slope deformation.