GPS measured static and kinematic offsets at near and far field of the 2011 Mw 9.0 Tohoku-Oki earthquake

The Mw 9.0 Tohoku-Oki earthquake that hit the mainland Japan on 11 th March, 2011 had resulted a devastating Tsunami due to an active thrusting between the Pacific and the North American Plates. Static and kinematic offsets at the offshore epicentre of the Mw 9.0 event remain unanswered and being investigated along with their near and far field limiting distances from the epicentre. Accordingly, offset measurements from 60 continuously operating IGS and GEONET GNSS stations were radially classified from the epicentre and interpreted with analytical models to find their linear offset decay rates. Co-and post-seismic static positional anomaly offsets of sixty days show almost all near field stations had strong or appreciable eastward or south eastward static shifts. Near stations(<250 km) showed both kinematic and static offsets. GEONET station ’0175’ showed maximum resultant static offset of-4.5 m, which diminishes approximately 1-2 cm at far sites like SMST and AIRA. Characteristic decay duration(’b’) of the mean kinematic co-seismic shift(’a’)of near field stations was 17.28 s during earthquake hours with an EW component shift >1.5 m. Spatial models of projected N-S static and kinematic offsets show their asymmetrical distributions around the epicentre with maximum model offset of-1.84 m displaced towards south at-45 km north of the epicentre. The Tohoku-Oki earthquake produced a resultant kinematic offset of-10.2 m towards East at its offshore epicentre;while the estimated near field static offset is ~9.82 m. However, both estimates are bigger than double the resultant offset measured value(~4.3 m) in the Japanese mainland using GPS. The difference in the kinematic and static near field offsets highlight that the near surface had elastic or in-elastic kinematic strain dissipation as against the lithospheric level viscoelastic static response, which resulted rapid kinematic strain release(1.12 cm/km)within the limiting radius of ~220 km from the Tohoku-Oki epicentre.

Impact assessment of the seasonal hydrological loading on geodetic movement and seismicity in Nepal Himalaya using GRACE and GNSS measurements

The Himalayan terrain is an epitome of ongoing convergence and geodetic deformation where both tectonic and non-tectonic forces prevail.In this study,the Gravity Recovery and Climate Experiment(GRACE)and Global Positioning System(GPS)datasets are used to assess the impact of seasonal loading on deformation with seismicity in Nepal.The recorded GPS data from 21 Global Navigation Satellite System(GNSS)stations during 2017-2020 are processed with respect to ITRF14 and the Indian reference frame,and the Center for Space Research(CSR)mascon RL06 during 2002-2020 is adopted to estimate the terrestrial water storage(TWS)change over the Ganga-Brahmaputra River basin.The results indicate that the hydrological loading effect or TWS change shows high negative,high positive,and moderately positive values in pre-monsoon,co-monsoon,and post-monsoon months,respectively.The detrended GPS data of both horizontal and vertical components correlate with the seasonal TWS change using the Pearson correlation coefficient at each GNSS site.In addition,the correlation coefficient has been interpolated using inverse distance weighting to investigate the regional TWS influence on geodetic displacement.In the north component,the correlation coefficient ranges from-0.6 to 0.6.At the same time,the TWS is positively correlated with geodetic displacement(0.82)in the east component,and the correlation coefficient is negative(-0.69)in the vertical component.The negative correlation signifies an inverse relationship between seasonal TWS variation and geodetic displacements.The strain rate is estimated,which shows higher negative values in pre-monsoon than in post-monsoon.Similarly,the effect of seismicity is 47.90%for pre-monsoon,15.97%for co-monsoon,and 17.56%for post-monsoon.Thus we can infer that the seismicity decreases with the increase of seasonal hydrological loading.Furthermore,the effect of strain is much higher in pre-monsoon than in post-monsoon since the impact of co-monsoon continues to persist on a small scale in the post-monsoon season.