Early magnitude and potential damage zone estimates for the great Mw 9 Tohoku‐Oki earthquake

Abstract

[1] The Mw 9.0, 2011 Tohoku-Oki earthquake has reopened the discussion among the scientific community about the effectiveness of earthquake early warning for large events. A well-known problem with real-time procedures is the parameter saturation, which may lead to magnitude underestimation for large earthquakes. Here we measure the initial peak ground displacement and the predominant period by progressively expanding the time window and distance range, to provide consistent magnitude estimates (M = 8.4) and a rapid prediction of the potential damage area. This information would have been available 35 s after the first P-wave detection and could have been refined in the successive 20 s using data from more distant stations. We show the suitability of the existing regression relationships between early warning parameters and magnitude, provided that an appropriate P-wave time window is used for parameter estimation. We interpret the magnitude under-estimation as a combined effect of high-pass filtering and frequency dependence of the main radiating source during the rupture process. Citation: Colombelli, S., A. Zollo, G. Festa, and H. Kanamori (2012), Early magnitude and potential damage zone estimates for the great Mw 9 Tohoku-Oki earthquake, Geophys.

Evidence for a difference in rupture initiation between small and large earthquakes

“…The P-wave onset times were manually selected from each vertical component of the accelerometer records. We measured the peak displacement amplitude on the filtered P-wave signals (P d ) over a progressively expanding PTW, starting from 0.05 s after the P-wave onset time and continuing until the expected arrival of the S-phase 30 . For each event, we obtained the LPW curve by averaging all the available data at each time window after correcting the observed P d values at different stations for the geometrical attenuation effect.…”

Source Parameter Estimation Method for Assessment of Structural Resiliencies

“…In the case of the Wenchuan 8.0 mainshock, using the first 3-second P wave may underestimate the magnitude by about 0.8 to 1.0 unit with the investigated parameters ( MI Ref = 7.18, = 7.05, and Ref = 6.91); however, the proposed MI was of the best performance. To mitigate this problem, several methodologies use a longer time window of P wave to update magnitude estimates [17,19]. The evolutionary estimation of MI as a function of the time window shows that the existing methodologies and regression relationships can be extended to large earthquakes, and the saturation effect can be removed through the use of time windows of approximately 6-7 seconds with the investigated MI parameter.…”

“…For the saturation problem in predicting large earthquakes, theoretically, a trade-off strategy between time and accuracy can be considered where better estimations could be obtained by enlarging the observation time window to update the characteristic parameters [15][16][17]. Since our proposed MI had the most accurate estimation for the mainshock with 3-second P wave compared with and , we further Frequency distribution histograms and the corresponding probability density curves of the estimated magnitude differences using each of the 3 characteristic parameters.…”

Self‐contained local broadband seismogeodetic early warning system: Detection and location

“…This was the upper limit of magnitude scaling in the near‐source region, and thus, an accurate magnitude was unavailable until the seismic waves were recorded at teleseismic distances. After the fact, Colombelli et al [] used seismic instrumentation to estimate the magnitude, achieving M w =8.4 after 35 s. However, the true M w 9.0 is still 8 times larger than M w 8.4 in terms of energy release; so while this result represents an improvement, it is still a significant underestimation.…”