2:15 PM - 2:30 PM
[SCG40-03] Interseismic coupling on the Main Himalayan Thrust in Nepal derived from GNSS displacement rate field
Keywords:Nepal, GNSS, NERDiM
Most of the land in Nepal is located on the hanging wall of the Indian-Eurasian plate convergent zone. We have deployed 10 continuous GNSS stations in central and mid-western Nepal since 2016 under the SATREPS/NERDiM project to enhance spatial resolution of geodetic observation network and better estimate earthquake generation potential in the Himalayan Frontal Zone (Silwal et al., 2021; this meeting). We focus especially on the “Central Seismic Gap” where no destructive event has been recorded for centuries. Data collected at each SATREPS/NERDiM GNSS site are transmitted to Kathmandu on a semi-daily basis via domestic cell phone network and then processed together with data from the pre-existing domestic GNSS stations and IGS reference stations. Highly automated data acquisition and baseline analysis system is implemented in a processing server.
As a preliminary analysis, we collect all available GNSS data in Nepal since 1995 through UNAVCO DAI v2 and process them using PPP-AR method of GIPSY/OASIS II ver.6.4. The result shows that the north-south contraction in Nepal is roughly 10-15 mm/yr, equivalent to a strain rate of 0.1 ppm/yr, implying that about 30-40% of the relative Indian-Eurasian plate motion (36-37 mm/yr) is taken up in crustal shortening across the Himalayan Frontal Zone. Next we estimate interseismic coupling on the Indian-Eurasian plate boundary using TDEFNODE (McCaffrey, 2009) and GNSS site displacement rates. Two plate boundary models are checked, the first one is characterized by down-dip variation of gently dipping fault planes and steeper ramps (Hubbard et al., 2016) and the second by rather flatter surface (Hayes, 2018). We constrain the lower limit of the plate interface to 35 km in depth and place nodes on the interface with a lateral spacing of 30-40 km along depth contours every 5 km. Then slip deficit rates are estimated on the interface. Plate coupling ratio (normalized slip deficit rate) seems corelate with structure of the interface, i.e., strong coupling on the gently dipping fault planes and week or null coupling on the steeper ramps. This pattern is in contrast with the previous result that shows coupling ratios nearly monotonously decreasing with depth on the flatter interface (e.g. Stevens and Avouac, 2015). Further investigation is needed to clarify current state of plate coupling on the Himalayan Frontal Zone.
As a preliminary analysis, we collect all available GNSS data in Nepal since 1995 through UNAVCO DAI v2 and process them using PPP-AR method of GIPSY/OASIS II ver.6.4. The result shows that the north-south contraction in Nepal is roughly 10-15 mm/yr, equivalent to a strain rate of 0.1 ppm/yr, implying that about 30-40% of the relative Indian-Eurasian plate motion (36-37 mm/yr) is taken up in crustal shortening across the Himalayan Frontal Zone. Next we estimate interseismic coupling on the Indian-Eurasian plate boundary using TDEFNODE (McCaffrey, 2009) and GNSS site displacement rates. Two plate boundary models are checked, the first one is characterized by down-dip variation of gently dipping fault planes and steeper ramps (Hubbard et al., 2016) and the second by rather flatter surface (Hayes, 2018). We constrain the lower limit of the plate interface to 35 km in depth and place nodes on the interface with a lateral spacing of 30-40 km along depth contours every 5 km. Then slip deficit rates are estimated on the interface. Plate coupling ratio (normalized slip deficit rate) seems corelate with structure of the interface, i.e., strong coupling on the gently dipping fault planes and week or null coupling on the steeper ramps. This pattern is in contrast with the previous result that shows coupling ratios nearly monotonously decreasing with depth on the flatter interface (e.g. Stevens and Avouac, 2015). Further investigation is needed to clarify current state of plate coupling on the Himalayan Frontal Zone.