Slip Model Of The 2016 Kumamoto,Japan Earthquake Of Mw7.0 Derived From Near-source Strong Motion,GPS And InSAR Data

Tens of thousands of earthquakes occur around the world every year.The abruptness and instantaneity of earthquakes often bring unpredictable disasters to people.Rapid access to scientific and accurate earthquake information,and make reasonable earthquake emergency response strategy,can be timely targeted emergency rescue,so as to avoid greater damage.The distribution characteristics of the surface co-seismic displacement field can reveal the damage scope and degree of the earthquake,which is of important reference significance for post-earthquake emergency rescue.It can be used to invert the slip distribution,understand the rupture process of the earthquake,and understand the gestation,development and occurrence law of the earthquake.The co-seismic displacement field can be obtained by using space geodetic techniques such as global positioning system(GPS),interferometric synthetic aperture radar(In SAR),or by solving the near-source strong motion acceleration recording.However,GPS and In SAR solutions are complex and take a long time,which usually takes days,weeks or even longer.For events that require rapid earthquake hazard assessment and early warning,this approach does not allow for time.The near-field acceleration records can be transmitted in real time or quasi-real time,and the co-seismic displacement field can be solved quickly,and then the sliding distribution can be inverted,which creates conditions for earthquake hazard assessment in time.Due to low-frequency interference(field background noise and instrument noise),instrument problems(magnetic hysteresis phenomenon),and ground tilting or rotation at near-source observation points,the velocity and displacement obtained by integration of acceleration recording have obvious baseline drift.In this paper,automatic empirical baseline correction program SMBLOC was used to baseline correction for the 94 strong motion stations' near-source acceleration records of kumamoto earthquake and obtain co-seismic displacement data.Compared with 57 near-field GPS coseismic displacement data,the movement direction and amplitude of the two data are in good agreement.It can be seen that the strong earthquake acceleration records can be used for baseline correction and the reliability of coseismic displacement data can be obtained.The seismogenic fault of Kumamoto earthquake is the Futagawa-Hinagu fault zone,and the strike of the two faults is obviously different.A single fault may not be able to accurately reflect the slip trend of the epicenter,but it is easier to obtain more accurate slip results by finely dividing the fault and inverting.Therefore,this paper uses GPS displacement data,In SAR data and the calculated displacement data of strong earthquakes to invert the source slip distribution of Kumamoto earthquake separately and jointly by using a single fault model and a double fault model,and the inversion results have high consistency.However,the slip range of double faults is wider,the moment magnitude is more concentrated,and the result of numerical simulation is better.This paper not only verifies the feasibility and rapidness of applying near-source acceleration records to earthquake rapid emergency response,but also constrains the slip distribution of Kumamoto earthquake,and the obtained results are closer to the real earthquake situation.The main understanding is as follows:1.On the whole,the distribution of GPS observations is basically consistent with the distribution of strong motion displacement field obtained by calculation,and the movement direction and amplitude of the station are roughly the same;Both GPS and strong motion show obvious four-quadrant symmetric distribution bounded by fault zones.The epicentre is stretched outwards in the northwest and southeast directions,while the northeast and southwest directions converge inwards,indicating that the fault dislocation of the earthquake is mainly right-lateral strike-slip mechanism.The peak slip of Kumamoto earthquake is not near the epicentre,but relatively far away from the epicentre.Along the two ends of the fault zone.There is a big difference in horizontal and vertical direction,that is the slippage of the northeast end is large,and the slippage of the southwest end is obviously weak,so the earthquake is in the northeast direction of the epicentre as the main rupture area.2.By comparing 12 pairs of GPS-strong motion stations with similar positions,it is found that when the displacement is larger than 2cm,the GPS and strong motion displacement direction and amplitude are relatively close.When the displacement is smaller than 2cm,there are many differences between GPS and strong motion displacement,which may be related to inaccurate baseline correction of strong motion data due to too small value.3.By using GPS observations,In SAR data and calculated strong motion displacement data independently and jointly,using a single fault model to invert the slip distribution.The results all show that the earthquake is mainly right-lateral strike-slip mechanism with a few positive fault characteristics.The earthquake has obvious the characteristic of double event rupture,and the amplitude of the first rupture is smaller than that of the second.The main rupture location is between 10 and 25 kilometers northeast of the epicentre,and the peak slip is between 4.01 and 5.85 meters.Moment magnitudes ranged from 7.07 to 7.13.4.By using GPS observations,In SAR data and strong motion displacement data independently and jointly,using a double fault model to invert the slip distribution.The results show that the earthquake is mainly right-lateral strike-slip mechanism with a few positive fault features which are mainly concentrated on fault plane A.The earthquake has obvious the characteristic of double event rupture,and the main fracture is located at fault plane A,the maximum slippage is between 4.66-6.04 meters.Relatively large slippage is located near the epicenter which is at fault plane B,and the maximum slippage is between 2.31-4.41 meters.The moment magnitude ranged from 7.08 to 7.11.Compared with the single fault model,the double-fault model has a larger slip range,a more concentrated moment magnitude range and a higher degree of numerical simulation,so it can be considered that the double-fault model is closer to the real situation.