Study On Crustal Deformation Of Earthquake And Tectonic Characteristics Using GPS And InSAR Data

Determining the magnitude and spatial distribution of fault slip is an important part of seismic study.Coseismic slip can help to clarify the geometric,strength and fric-tion characteristics of active faults,and can be used to estimate the area near the fault zone where the stress is partially released and the area where the stress is maintained or increased.These can be used as an indicator to judge whether the fault or nearby fault area is close to or far from rupture.The same inversion method can also be used to monitor the postseismic and interseismic slip,and to help infer the distribution and proportion of off-fault deformation,so as to understand the earthquake cycle.Fault slip values are also widely used to estimate the magnitude of paleoearthquakes.The Interferometric Synthetic Aperture Radar(InSAR),combined with satellite acquisition before and after an earthquake,provides spatially intensive observations of surface dis-placement and,together with Global Positioning System(GPS)observations,can be used to invert fault slip,magnitude and earthquake location caused by an earthquake.With the European Space Agency new satellites,Sentinel-1A and Sentinel-1B,provid-ing unprecedented ground repeat observations,the scientific community can now use InSAR to regularly monitor all large continental earthquakes,and fault slip distribution inversion is a key part of this process.I firstly introduces the basic concept of GPS and satellite radar observation tech-nology,the principle of correlation observation and its application in study on crustal deformation of earthquake,and expounds the fault inversion theory to determine the fault slip distribution and the related method of selecting the relative weight and smooth factor.Secondly,joint inversions of SAR and GPS measurements are used to investigate the source parameters of four Mw>5 events of the 2016–2017 Central Italy earthquake sequence.The results show that the four events are all associated with a normal fault striking northwest–southeast and dipping southwest.The observations,in all cases,are consistent with slip on a rupture plane,with strike in the range of 157°to 164°and dip in the range of 39°to 44°that penetrates the uppermost crust to a depth of0 to 8 km.The primary characteristics of these four events are that the 24 August2016 Mw6.2 Amatrice earthquake had pronounced heterogeneity of the slip distribution marked by two main slip patches,the 26 October 2016 Mw6.1 Visso earthquake had a concentrated slip at 3–6 km,and the predominant slip of the 30 October 2016 Mw6.6Norcia earthquake occurred on the fault with a peak magnitude of 2.5 m at a depth of0–6 km,suggesting that the rupture may have reached the surface,and the 18 January2017 Mw5.7 Campotosto earthquake had a large area of sliding at depth 3–9 km.The positive static stress changes on the fault planes of the latter three events demonstrate that the 24 August 2016 Amatrice earthquake may have triggered a cascading failure of earthquakes along the complex normal fault system in Central Italy.Thirdly,I used Sentinel-1 InSAR data to investigate coseismic deformation asso-ciated with the 2017 Sangsefid earthquake,which occurred in the southeast margin of the Kopeh Dagh fault system.The ascending and descending interferograms indicate thrust-dominated slip,with the maximum line-of-sight displacement of 10.5 and 13.7cm,respectively.The detailed slip distribution of the 2017 Sangsefid Mw6.1 earthquake inferred from geodetic data is presented here for the first time.Although the InSAR interferograms themselves do not uniquely constrain what the primary slip surface is,we infer that the source fault dips to southwest by analyzing the 2.5D displacement field decomposed from the InSAR observations.The determined uniform slip fault model shows that the dip angle of the seimogenic fault is approximately 40°,with a strike of120°except for a narrower fault width than that predicted by the empirical scaling law.We suggest that geometric complexities near the Kopeh Dagh fault system obstruct the rupture propagation,resulting in high slip occurred within a small area and much higher stress drop than global estimates.The InSAR-determined moment is 1.71×10¹⁸Nm with a shear modulus of 3.32×10¹⁰N/m²,equivalent to Mw6.12,which is consistent with seismological results.The finite fault model(the west-dipping fault plane)reveals that the peak slip of 0.90 m occurred at a depth of 6.3 km,with substantial slip at a depth of 4–10 km and a near-uniform slip of 0.1 m at a depth of 0–2.5 km.We sug-gest that the Sangsefid earthquake occurred on an unknown blind reverse fault dipping southwest,which can also be recognised through observing the long-term surface effects due to the existence of the blind fault.Fourthly,I used GPS time series to investigate the temporal-spatial variations of postseismic deformation after Nepal earthquake.Surface displacements measured with the GPS during the 310 days after 2015 Nepal Mw7.8 earthquake indicate high slip rates surrounding the region of the greatest coseismic rupture and downdip propagation to the deeper with a slower decay rate.We find horizontal motion of up to about 75mm in a southward direction similar to that of the coseismic displacements,while the postseismic vertical displacement of near-field stations have reversed the direction of coseismic displacements except the station NAST.Elastic triangle dislocation model inversions for the temporal and spatial variations of the afterslip and slip rate,using a Network Inversion Filter method(NIF),shows the highest afterslip rate located under the regions of the major coseismic slip.The maximum slip rate occurs on the fifteen days following the main shock and the slip rate tends to steady in the late stage.The average slip rate increases rapidly and begins to decay after the largest Mw7.3 aftershock.The maximum afterslip occurs below the region of the coseismic rupture and near the Nepal hypecenter.The effect of viscoelastic relaxation is also simply estimated and the results show that the influence during the first three hundred and ten days is small.The process of forming the concentrated slip distribution is investigated from the perspective of slip rates.During the first three hundred and ten days after the mainshock,the total accumulated geodetic slip moment is 1.46×10²⁰Nm,assuming a shear modulus of3×10¹⁰P a,equivalent to a moment magnitude of 7.41.The average slip rate shows that the afterslip will continue.At last,I used Sentinel-1 radar imagery to explore the coseismic and postseismic surface displacements associated with the 2016 Mw6.2 Lampa earthquake in southern Peru.Here we present the first results that provide insights into the seismogenic struc-ture of the earthquake.Based on coseismic interferograms,the preferred slip model links to a blind SSE-striking,SSW-dipping plane with a shallow dipping(44°)and a peak slip of 0.76 m at depth 5.2 km,which is consistent with seismic solutions.Postseismic interferograms,derived from 2 tracks of the Sentinel-1A/B satellites using a small base-line subset method,show subsidence up to 3 cm in the first year after the mainshock.The kinematic inversions of InSAR data imply that the postseismic surface displace-ments observed in one year after the earthquake are governed by afterslip occured along the updip extension of the coseismic slip patches.The stress-driven afterslip forward modeling shows that the postseismic deformation is controlled by afterslip distributed at the edge of the compacted coseismic slip area.The surface displacement predictions of the poroelastic rebound show subsidence of the hanging wall,but the order of the magnitude is small.We as well test a collection of viscoelastic relaxation models and find that the predicted surface displacements are not consistent with the observations.Based on results of the analysis,we suspect that the causative fault of this 2016 event may be a new normal fault generated in a'domino'faulting system.