Rapid coseismic fault determination of consecutive large interplate earthquakes: The 2011 tohoku-oki sequence

Real-time monitoring of crustal deformation is important in achieving rapid understanding of earthquake magnitude and fault model. Recently, an algorithm called Real-time Automatic detection method for Permanent Displacement (“RAPiD”) has been developed to detect/estimate static ground displacements due to earthquake faulting from real-time kinematic (RTK)-GPS time series. We applied this algorithm to the 2011 off Ibaraki earthquake (M_w 7.7), which occurred only 30 min after the 2011 Tohoku-Oki earthquake (M_w 9.0). The RAPiD algorithm worked well with the long baseline RTK-GPS time series for quasi real-time coseismic displacement detection and estimation. A quasi real-time fault determinationwas also attempted with an automatic detection/estimation displacement field. We found that the estimated moment release reached M_w 7.7 60 s after the origin time, almost the same as the actual seismic moment for this earthquake. We also assessed the long-term stability of the RTK-GPS time series under a 200-km baseline condition. We found the time series precision degraded slightly in summer compared with winter. However, the total stability is good for monitoring crustal deformation. These results suggest clearly that using real-time GPS data in conjunction with the RAPiD algorithm can provide rapid coseismic fault determination, even for consecutive large earthquakes.