Seasonal Modulation of Deep Slow-slip and Earthquakes on the Main Himalayan Thrust

Abstract

The interaction between seasonally-induced non-tectonic and tectonic deformation along the Himalayan plate boundary remains debated. Here, we propose that tectonic deformation along this plate boundary can be significantly influenced by the deformation induced by the non-tectonic hydrological loading cycles. We explore seasonal mass oscillations by continental water storage in Southeast Asia and Himalayan arc region using continuous Global Positioning System measurements and satellite data from the Gravity Recovery and Climate Experiment. We suggest that the substantially higher transient displacements above the base of the seismogenic zone indicate a role of changes in aseismic slip rate on the deep megathrust that may be controlled by seasonal hydrological loading. We invoke modulation of aseismic slip on the megathrust down-dip of the seismogenic zone due to a fault resonance process induced by the seasonal stress changes. This process modulates mid-crustal ramp associated micro-seismicity and influences the timing of Central Himalayan earthquakes.

Active tectonics of Himalaya, rift basins in Central India and those related to crustal deformation at different time scales

“…The seasonal variation is relatively more in vertical as compared to horizontal displacement components . Panda et al (2018c), have mentioned that the continuous GPS measurements in the Uttarakhand and Nepal Himalaya show relatively higher transient displacement above the base of the seismogenic zone which is the response of modulation in aseismic slip rate on the deep megathrust controlled by the seasonal hydrological load. It is observed that shear-stress perturbations induced by the seasonal hydrological load are about three times larger on the mid-crustal ramp than on the up-dip flat segment of MHT.…”

“…The thrusts tectonically dividing five litho-tectonic zones of the Himalaya, i.e., Trans-Himalaya, Tethyan Himalaya, Higher Himalaya, Lesser Himalaya, and the Sub-Himalaya, are the Main Central Thrust (MCT), Main Boundary Thrust (MBT) and the Main Frontal Thrust (MFT) in Nepal or Himalayan Frontal Thrust (HFT) in India. These tectonic structures merge into a lowangle crustal decollement thrust sheet called the Main Detachment Fault (MDF) (Panda et al, 2018c;Sreejith et al, 2018), which later modified to Main Himalayan Thrust (MHT) based on observations from the INDEPTH project seismic reflection profiles. The MFT (also known as Himalayan Frontal Thrust or HFT) is a physiographic and tectonic boundary between the Ganga-Brahmaputra alluvial plains and the Tertiary Siwaliks of the Sub-Himalaya .…”

Reply to “A warning against over-interpretation of seasonal signals measured by the Global Navigation Satellite System”

“…The anomalous transients reported by Panda et al 1 are observed at some of the GNSS sites that are located above the base of the seismogenic fault, i.e., the Main Himalayan Thrust (MHT). There is evidence that a mid-crustal ramp close to the base of the seismogenic MHT may only exist on some Himalayan sections 5,6 .…”

“…anda et al 1 analysed 41 continuous Global Navigation Satellite System (GNSS) sites from the Nepal and Garhwal-Kumaun region of the Himalayan arc and found that a few sites, which are located northward about 100 ± 20 km from the Main Frontal Thrust, show higher-amplitude seasonal transients in the horizontal component (predominantly in the north) of the GNSS coordinate time series. They ascribed these transients to changes in aseismic slip rate on the deep megathrust that may be controlled by seasonal hydrological loading 1 . They further invoked that modulation of aseismic slip on the megathrust down-dip of the seismogenic zone is due to the fault resonance process, induced by the seasonal hydrological stress changes.…”

“…There is evidence that a mid-crustal ramp close to the base of the seismogenic MHT may only exist on some Himalayan sections 5,6 . Panda et al 1 argued that the GNSS sites above or close to the ramp may exhibit higher transient motion near regions where subsurface fluids are abundant at the MHT. Fluids at high pressure are commonly invoked to explain the slow-slip transients occurring at deeper level on continental and subduction faults around the world [7][8][9] .…”