An Improved Rapid-Source Parameter Determination System (AQUA) for Giant Earthquakes

This article describes improvement of the rapid earthquake analysis system, accurate and quick analysis system for source parameters (AQUA), which has automatically determined the location, magnitude, and fault type of M <; ~7 earthquakes with good accuracy by analyzing long-period waveform data, but could not process the 2011 Off Tohoku giant earthquake (M9.0) due to instrumental and program limitations. Here, we address these problems by incorporating strong-motion seismic data and changing processing parameters accordingly, which extends the upper limit of applicable magnitudes to M9. In a simulated process, this earthquake is properly determined as thrust faulting with M8.6 offshore northeast Japan within 431 s of the first phase arrival. We also evaluate its performance. After improvements, four recent large earthquakes (M7.0-7.9) were properly processed in real time. The successful determination ratio is 100% for events with Japanese seismic intensity ≥6 Lower, and 100% for events with M>7 except nearly simultaneous events. Source parameters with and without fixed horizontal locations are provided within 100-250 and 100-600 s of the first P arrival, respectively. This system is valuable for disaster mitigation because it rapidly provides information for use in tsunami warning and early damage assessment.