Segmentation of the Himalayas as revealed by arc-parallel gravity anomalies

Abstract

Lateral variations along the Himalayan arc are suggested by an increasing number of studies and carry important information about the orogen’s segmentation. Here we compile the hitherto most complete land gravity dataset in the region which enables the currently highest resolution plausible analysis. To study lateral variations in collisional structure we compute arc-parallel gravity anomalies (APaGA) by subtracting the average arc-perpendicular profile from our dataset; we compute likewise for topography (APaTA). We find no direct correlation between APaGA, APaTA and background seismicity, as suggested in oceanic subduction context. In the Himalayas APaTA mainly reflect relief and erosional effects, whereas APaGA reflect the deep structure of the orogen with clear lateral boundaries. Four segments are outlined and have disparate flexural geometry: NE India, Bhutan, Nepal & India until Dehradun, and NW India. The segment boundaries in the India plate are related to inherited structures, and the boundaries of the Shillong block are highlighted by seismic activity. We find that large earthquakes of the past millennium do not propagate across the segment boundaries defined by APaGA, therefore these seem to set limits for potential rupture of megathrust earthquakes.

Imaging the Moho and the Main Himalayan Thrust in Western Nepal With Receiver Functions

“…In Western Nepal, the distance over which the Moho reaches its maximum depth differs from Central Nepal (Figure ; Nábělek et al, ): The gentler descent ends further north, north of the Higher Himalaya, at nearly 80‐km depth beneath southern Tibet (Xu et al, ). This may reflect a slightly different flexural rigidity of the India plate in Western Nepal compared to Central Nepal, although there is no significant difference in flexure West and East of our profile in Nepal as seen by gravity anomalies and numerical modeling (Berthet et al, ), unlike further toward NW India and to the Eastern Himalaya (Hammer et al, ; Hetényi, Cattin, et al, ; Lyon‐Caen & Molnar, ).…”

Geometry of the Main Himalayan Thrust and Moho beneath Satluj valley, northwest Himalaya: Constraints from receiver function analysis

“…Underthrusting bathymetric features like the DHR (Figure ) can change the crustal configuration and geometry of the MHT as observed in this study. Lateral segmentation of subsurface structures in the Himalaya is revealed by arc‐parallel gravity anomaly [ Hetényi et al , ]. The seismicity pattern in the HSB in Satluj valley and in the adjacent Garhwal Himalaya clearly reflects the role of the ramp structure on the MHT in the generation of clustered seismicity [ Caldwell et al , ].…”

“…Significant along‐strike variations in topography and relief [ Duncan et al , ], convergence and shortening rates [ Banerjee and Bürgmann , ; Paul et al , ], and exhumation rates [ Robert et al , ] are also reported. Recent high resolution gravity data also reveal lateral segmentation of subsurface structure in the Himalaya [ Hetényi et al , ]. Seismicity studies suggest along‐strike variation in the northwest Himalaya [e.g., Gahalaut and Kalpna , ; Arora et al , ].…”

Joint approach combining damage and paleoseismology observations constrains the 1714 A.D. Bhutan earthquake at magnitude 8 ± 0.5

“…Although the characteristics (rupture geometry and intensity attenuation) of a given M ~ 8 earthquake may naturally deviate from statistically determined averages, our results seem not to contradict any known observation and seem to be credible for this 300 year old event. The along‐arc location and potential extent of the earthquake also conforms to the segmentation of the Himalayas as revealed by arc‐parallel gravity anomalies [ Hetényi et al ., ].…”