Outline of the 2011 off the Pacific coast of Tohoku Earthquake (M w 9.0) —Earthquake Early Warning and observed seismic intensity—

Abstract

The 2011 off the Pacific coast of Tohoku Earthquake (M w 9.0) that occurred on March 11, 2011, caused strong ground motion around northeastern Japan. Before the strong ground motion hit cities, the Japan Meteorological Agency (JMA) issued Earthquake Early Warning (EEW) announcements to the general public of the Tohoku district and then the warning was automatically broadcast through TV, radios and cellular phone mails. The EEW was earlier than the S wave arrival and more than 15 s earlier than the strong ground motion (intensity 5-lower or greater on the JMA scale) everywhere in the district. Seismic intensity 7 was observed for only the second time since JMA introduced instrument-based observation for intensity measurements in 1996. Intensities of 6-upper and 6-lower were widely observed at many stations in the Tohoku and Kanto districts, over an area of approximately 400 km × 100 km. The duration of strong ground motions was quite long. For the Tokyo region, JMA EEW expected intensities of 4, which was an underestimation of the observed intensity (5-upper). This underestimation can probably be attributed to the large extent of the fault rupture.

Seismic Constraints on a Double‐Layered Asymmetric Whole‐Mantle Plume Beneath Hawai‘i

“…Earthquake early warning (EEW) systems are essential in mitigating seismic hazard by issuing warnings prior to the arrival of strong ground shaking during an earthquake� Many of the currently operating EEW systems work on the basis of magnitude-amplitude/frequency scaling for a point source, which is invalid for magnitude estimation of M >7�5 earthquakes� This issue is particularly highlighted in EEW performance of the M9�0 Tohoku-Oki earthquake (Hoshiba et al, 2011)� Failing to take into account the finite rupture propagation, the magnitude estimated by the Japanese EEW system saturated at M8�1� The Japanese Meteorological Agency (JMA) issued warnings of strong seismic intensity only for the Tohoku region� However, the Kanto region experienced much larger ground motions than that predicted by JMA� The example of the Tohoku-Oki earthquake demonstrates the need for characterizing the finite fault dimension in real time for EEW systems of large earthquakes to be successful� Among the ongoing efforts to determine the finite fault extent in real time, GPS approaches provide more reliable static displacements and thus, magnitude, than do seismic methods (Colombelli et al, 2013)� The FinDer approach is also proposed to determine linear fault geometry based on the amplitude difference in near/far field seismic waveform, provided dense station coverage� Alternatively, we explore the concept of imaging the rupture process of large earthquakes in real time using clusters of dense seismic arrays located near an active fault� Back tracing the waveforms of earthquakes recorded by such arrays allows the estimation of the rupture directivity, size, duration, speed, and segmentation, which enables the EEW of M>6 earthquakes� The principle is analogous to the location and tracking of moving sources by antennas in a variety of military and civilian applications� Figure 2�34�1 illustrates the concept of seismic array processing for EEW� Strong, high-frequency (HF) seismic waves usually radiate from the rupture front� Tracking the source of the HF seismic waves during large earthquakes recovers the movement of the rupture front� The trajectory of the rupture front marks the fault extent involved in the earthquake�…”

Optimal Seismic Network Density for Earthquake Early Warning: A Case Study from California

“…Probing the way business and the public actively use early warning information is a crucial factor in early warning system design (Aktas et al, 2010;Kuyuk, 2010;Kuyuk et al, 2008;Nakamura, 1988). During the 2011 M 9 Tohoku-oki, Japan, earthquake, an earthquake warning was successfully issued although the magnitude was underestimated (Hoshiba et al, 2011). To determine the usefulness of the alerts, the Japan Meteorological Agency (JMA) conducted a public survey (JMA, 2012).…”

Detection and mapping of soil liquefaction in the 2011 Tohoku earthquake using SAR interferometry

“…In the Kanto region including Tokyo, about 350 km from the mainshock, seismic intensities of 5-lower to 6-lower were recorded ( Fig. 1(a)) (Hoshiba et al, 2011). There were large areas of soil liquefaction, especially along Tokyo Bay and the Tone River, causing extensive damage to residential buildings and infrastructure (Bhattacharya et al, 2011;Yasuda and Harada, 2011;Senna et al, 2012).…”