Seasonal modulation of deep slow-slip and earthquakes on the Main Himalayan Thrust

Gravity-induced seismicity modulation on planetary bodies and their natural satellites

Ground-based monitoring of seismicity and modulation by external forces in the field of planetary seismology remains equivocal due to the lack of natural observations. Constrained by the natural observations (including Earthquakes, Moonquakes, and Marsquakes) and theoretical models, we present the variation in gravitational acceleration "g" of different solar system objects, combined with external harmonic forcings that are responsible for seismicity modulation on the planetary bodies and their natural satellites. From the global diversity in seismicity modulation, it has been observed that the plate-boundary regions on the Earth exhibit both short and long-period seismicity modulation. In contrast, the stable plate interior regions appear to be more sensitive to long-period seismicity modulation, however, lacking in short-period modulation. The deep Moonquakes are susceptible for both the lunar tidal period (13.6 days and 27 days) and long-period pole wobble modulation (206 days), whereas shallow emergent type moonquakes show a seismic periodicity at the lunation period (29.5 days). Further, the seasonal variation with an annual seismicity burst and seismic periodicity at polar wobble periods for high-frequency Marsquakes captured by InSight lander indicate a natural origin. Whereas diurnal and semi-diurnal periodicity along with Phobos' tidal period, indicate possible artifacts due to different detection probabilities and non-seismic noise in the Martian environment. We argue that, in the context of rate-state-dependent fault friction, the gravity-induced resonance destabilization model appears to be better agreement with the contrast and relative diversity in seismicity modulation linked to the Earth, Moon, and Mars.

Groundwater extraction-induced seismicity around Delhi region, India

The non-tectonic deformation, either of natural or anthropogenic origin, may influence the earthquake occurrence process and seismicity rate along the plate-boundary or ‘stable’ plate-interiors domains. The low magnitude but moderate seismicity rate of Delhi region on the stable plate-interiors domains of India, exhibits significant variation both in short-term at annual seasonal scale and in long-term at decadal scale. It correlates with the anthropogenic groundwater pumping for the extensive irrigation, urban activities, and seasonally controlled hydrological loading cycle of Indo-Ganga Basin hosted freshwater aquifers. Our coupled hydro-mechanical simulation and poro-mechanical analysis of basement fault stability suggest that the combined aquifer contraction and basement rock expansion act together to modulate the effective stress regime and anthropogenic seismicity on the basement faults in Delhi region.