17:15 〜 18:30
[SIT19-P03] Coseismic Fault Model for the Thabeikkyin earthquake in 2012 determined from GNSS Observation
キーワード：GNSS, Sagaing Fault, coseismic slip, Thabeikkyin earthquake
The Sagaing Fault, a right-lateral strike slip fault, slip rate 18 – 20 mm/yr, more than 1200km long which is north-south trending major active geological structure in Myanmar. Many significant historical earthquakes occurred along its fault. The recent 2012 Thabeikkyin earthquake, Myanmar occurred on 11 November 2012 at the Sagaing Fault in central Myanmar which claimed more than 20 fatalities and more than 200 injuries during in this earthquake.
The GNSS (Global Navigation Satellite System) network was constructed under the collaboration between Earth Observatory of Singapore (EOS), Myanmar Earthquake Committee (MEC), Department of Meteorology and Hydrology, Myanmar (DMH) and Myanmar Survey Department (MSD) in 2011. We calculated velocities of GNSS stations by using GIPSY-OASIS ver 6.4 software from Jet Propulsion Laboratory (JPL) with latest realization of the International Terrestrial Reference Frame 2014 (ITRF2014). Ocean tide loading was calculated using FES2014b model by the Onsala Space Observatory (http://holt.oso.chalmers.se/loading/) with respect to the joint mass center of solid Earth and ocean combined. We also collected data for nearby 8 International GNSS Service (IGS) stations and estimated velocities of these stations in our processing. We subtracted the average positions for 10 days before the 2012 Thabeikkyin earthquake and from those for 10 days after the main shock to obtain coseismic displacement from GNSS surveyed data. We utilize observed coseismic displacements from GNSS data to estimate the coseismic slip of the 2012 earthquake by using Okada’s (1992) elastic half-space dislocation model.
We estimate a rectangular fault model based on available GNSS continuous stations. In this study, we used two GNSS stations, SWBO and SDWN which recorded coseismic displacement during the earthquake. The calculated coseismic displacements show right lateral strike slip along the fault segment. SDWN showed large coseismic displacement up to 15 cm, while SWBO experienced 3.6 cm, respectively as shown in Fig. We assume a single fault plane with strike of 0°, dip 71° (east-dipping) and rake of 178° based on CMT solution and that the fault plane is aligned on the Sagaing Fault. We search for fault parameters using a non-linear inversion method of Matsu’ura and Hasegawa (1987). The initial parameters such as length, width, depth of the upper margin are assumed based on the field surface rupture length, that is, length: 45.185 km (SagaingFault.info), width: 10 km (Sun et al. 2013, Tun & Watkinson 2017, Hlaing et al. 2019) and depth: 0 km, respectively. The preliminary result of optimum geodetic data inversion suggested slip amount 1.5 m with seismic moment of 3.68 x 1019 Nm (Mw 6.9) and obtained fault size 46.8km x 17.2 km, at depth 2.3 km with strike 0°, 44° east-dipping, rake 190°, respectively. Our result of coseismic slip can explain very well the observed displacement of the Thabeikkyin earthquake although the available data is limited. Our estimated coseismic rectangle fault show east dipping which may be effected due to the clockwise rotation of the eastern himalayan synthesis in the northeastern part of Myanmar or roughly correspond to an intersection point of the Sagaing Fault, Momeik fault and Shan scarp fault zone.
Fig. Coseismic displacement of the 2012 Thabeikkyin earthquake. The black rectangle denotes the fault plane. Blue and pink arrows show observed and model displacement, respectively.
The GNSS (Global Navigation Satellite System) network was constructed under the collaboration between Earth Observatory of Singapore (EOS), Myanmar Earthquake Committee (MEC), Department of Meteorology and Hydrology, Myanmar (DMH) and Myanmar Survey Department (MSD) in 2011. We calculated velocities of GNSS stations by using GIPSY-OASIS ver 6.4 software from Jet Propulsion Laboratory (JPL) with latest realization of the International Terrestrial Reference Frame 2014 (ITRF2014). Ocean tide loading was calculated using FES2014b model by the Onsala Space Observatory (http://holt.oso.chalmers.se/loading/) with respect to the joint mass center of solid Earth and ocean combined. We also collected data for nearby 8 International GNSS Service (IGS) stations and estimated velocities of these stations in our processing. We subtracted the average positions for 10 days before the 2012 Thabeikkyin earthquake and from those for 10 days after the main shock to obtain coseismic displacement from GNSS surveyed data. We utilize observed coseismic displacements from GNSS data to estimate the coseismic slip of the 2012 earthquake by using Okada’s (1992) elastic half-space dislocation model.
We estimate a rectangular fault model based on available GNSS continuous stations. In this study, we used two GNSS stations, SWBO and SDWN which recorded coseismic displacement during the earthquake. The calculated coseismic displacements show right lateral strike slip along the fault segment. SDWN showed large coseismic displacement up to 15 cm, while SWBO experienced 3.6 cm, respectively as shown in Fig. We assume a single fault plane with strike of 0°, dip 71° (east-dipping) and rake of 178° based on CMT solution and that the fault plane is aligned on the Sagaing Fault. We search for fault parameters using a non-linear inversion method of Matsu’ura and Hasegawa (1987). The initial parameters such as length, width, depth of the upper margin are assumed based on the field surface rupture length, that is, length: 45.185 km (SagaingFault.info), width: 10 km (Sun et al. 2013, Tun & Watkinson 2017, Hlaing et al. 2019) and depth: 0 km, respectively. The preliminary result of optimum geodetic data inversion suggested slip amount 1.5 m with seismic moment of 3.68 x 1019 Nm (Mw 6.9) and obtained fault size 46.8km x 17.2 km, at depth 2.3 km with strike 0°, 44° east-dipping, rake 190°, respectively. Our result of coseismic slip can explain very well the observed displacement of the Thabeikkyin earthquake although the available data is limited. Our estimated coseismic rectangle fault show east dipping which may be effected due to the clockwise rotation of the eastern himalayan synthesis in the northeastern part of Myanmar or roughly correspond to an intersection point of the Sagaing Fault, Momeik fault and Shan scarp fault zone.
Fig. Coseismic displacement of the 2012 Thabeikkyin earthquake. The black rectangle denotes the fault plane. Blue and pink arrows show observed and model displacement, respectively.