Algorithm And Earthquakes Study Of Geodetic Inversion Based On Triangular Dislocation Element Model

Earthquake studies are usually related to multiple disciplines(e.g.,seismology and geodesy),which are strongly relied on observations from earthquakes themselves directly.Geodesy,mainly GNSS and InSAR,with over twenty years development since the early 1990 s,has become the most important skill to study earthquake kinematics and even earthquake dynamics,since it could obtain huge amount of surface deformation data with high precision in both space and time domain.Geodetic data applications to earthquake studies are broadly concerned but not limited to at least three aspects: 1)Deformation characteristics related to earthquake cycle;2)Coseismic fault slip and earthquake rupture process inversion;3)Probing deep earth rheologic structures through modeling postseismic deformation.To our best knowledge,coseismic slip inversion based on geodetic data and linear dislocation model is the most successful application of geodesy and has become the most intuitive method studying the faulting mechanism and dynamic rupture of earthquake.Most of previous published literatures use Okada model,which is a very popular dislocation model based on rectangular units.An important advantage of the Okada model is that it is easy and fast to implement coseismic slip inversion,if the earthquake source fault could be simplified as a single and planar fault plane.However,as lots of modern earthquake studies reveal,fault geometry of earthquake is often so complex with large variations in spatial domain that a single and planar fault plane is not sufficient to represent.When using Okada model and rectangular units in such complex fault geometry,we will get gaps or(and)overlaps in the fault model.Such gaps and overlaps will present obstacles to invert slip distribution in details and even lead confusions to earthquake faulting mechanism.With sufficient amount and higher precise of geodetic data,it is more appropriate to implement triangular dislocation element model,which can represent the continuity and smoothness of the fault geometry with no gaps and overlaps.Therefore,we develop a coseismic modeling code based on triangular dislocation element model(TDE)and implement a fast discretization method to construct complex fault geometry without gaps and overlaps.We compare the TDE forward modeling module code with the code based on Okada model and verify the reliability of the TDE code.Eventually,we use our code to study three different fault styles of strong earthquake,i.e.,the 2015 Illapel,Chile Mw8.3 earthquake,the 2015 Gorkha,Nepal,Mw 7.9 earthquake and the 2016 Kumamoto,Japan,Mw 7.0 earthquake.Our conclusions are as follow:1)We develop a TDE-based forward modeling code,according to an updated TDE-based analytic equations that are without singularities.And we make full verifications of the code through comparisons to modeling results of Okada model using simulated coseismic deformation data in different observing directions(east-west,north-south,vertical and line of sight of InSAR)with different faulting senses(strike slip,thrust or normal faulting).2)We implement a TDE-based discretization tool to represent the continuity and smoothness of complex fault geometry.Comparing with existing tools,our discretization tool is fast to establish a full TDE fault geometry model with complexities in both strikes and dips.More importantly,the tool can represents complex fault geometry without gaps and overlap that commonly exist in Okada model.3)We develop a TDE-based inversion code that can use geodetic data(GNSS or InSAR)to invert the fault slip distribution under complex fault geometry,based on constrained least square method.In addition,our inversion code can calculate the moment tensor and magnitude of the earthquake.4)Based on the check-board skill,we conduct full resolution test inversion to evaluate the TDE inversion code.Through comparisons with Okada-model-based inversion code,we verify the robustness and reliability of our TDE inversion code.5)Our TDE codes are eventually used to study three strong earthquakes with different faulting mechanisms.The 2015 Illapel,Chile,Mw 8.3 earthquake is an intercontinental earthquake occurred on subduction zone.The 2015 Gorkha,Nepal,Mw 7.9 earthquake is a continental thrusting earthquake.The 2016 Kumamoto,Japan,Mw 7.0 earthquake is a strike slip fault event.We gain new insights from the earthquake case studies with new satellite data of Sentinel-1A and new tool of TDE.