Magnitude determination using duration of high frequency energy radiation and displacement amplitude: application to tsunami earthquakes

The rapid determination of its magnitude soon after a great earthquake is necessary for the issuing of effective tsunami warnings, as demonstrated in the great earthquake off Tohoku district in Japan on March 11, 2011. The earthquake magnitude for the first tsunami warning was underestimated due to magnitude saturation. This paper proposes a method to determine magnitude rapidly from peak velocity and displacement of long-period seismic waves up to 100 seconds at local stations. When waveform data at local stations are available, the magnitude from S-wave peaks is expected to be determined faster than that from only P-wave peaks. It takes about 140 seconds to estimate a magnitude of about 9 for the March 11, 2011, earthquake, which would enable us to issue the first tsunami warning within three minutes after the same type of earthquake.

Section: Introductionmentioning

confidence: 99%

Rapid magnitude determination from peak amplitudes at local stations

Katsumata¹,

Ueno²,

Aoki³

et al. 2013

“…Tsunami earthquakes generate unusually large tsunami waves relative to their surface wave magnitudes (Kanamori, 1972) and are characterized by several common factors, such as long source durations, depletion in high-frequency radiation, and the proximity of their source region to the trench axis (e.g., Pelayo and Wiens, 1992;Polet and Kanamori, 2000;Hara, 2007). Thrust-faulting along the shallow part of the plate boundary is the candidate source of the tsunami earthquake.…”

Section: Introductionmentioning

confidence: 99%

Waveform inversion for slip distribution of the 2006 Java tsunami earthquake by using 2.5D finite-difference Green’s function

Okamoto

Takenaka

2009

We first incorporate the large effect of near-source heterogeneity on teleseismic body waveforms in the inversion of the slip distribution of the 2006 Java tsunami earthquake. We incorporate the effect by computing the response of an assumed "2.5D" model structure of the Java trench by a 2.5D finite-difference method. Based on a simulation of inversion, we suggest that intense smearing is possible when we apply 1D Green's functions in the analysis, and that it may obscure the slip pattern. In the inversion of real data, we confirm macroscopic features, such as a long duration (∼165 s) and a slow rupture velocity (∼1.25 km/s). The region of the initial rupture is found to be isolated from the eastern broad region in which we further identify a heterogeneous slip distribution. Most of these regions are likely to be at the sedimentary plate interface where the accreted sediment and the subducting plate are in contact. In particular, the nearly "isolated" feature of a shallow slip region suggests a possible faulting in the shallowest part of the sedimentary plate interface without being strongly enforced by the rupture propagated from the deeper part of the fault. Such heterogeneity suggests a highly variable frictional behavior at the sedimentary plate interface.

“…We have recently developed a method to determine earthquake magnitudes using durations of P-wave high-frequency energy radiation and maximum displacement amplitudes (Hara, 2007a). We have also shown that this method is applicable to tsunami earthquakes (Hara, 2007b).…”

Section: Introductionmentioning

confidence: 99%

Temporal characteristics of high band-pass filtered teleseismic P-waveforms from large shallow earthquakes

Hara

2008

Self Cite

We measured time differences between P-wave arrivals and the times at which squared amplitudes of high bandpass (2-4 Hz) filtered P-waves became the largest for large shallow earthquakes that occurred during the period 1995-2007. The time differences were then normalized by twice the centroid time shift for the corresponding earthquakes. We found that most of the seismograms had normalized time differences that congregated at about 50% (corresponding to centroid time shifts). Few normalized time differences were found in the 0-20% range. These results support the use of this time difference to infer the order of the source duration and, thereby, the effectiveness of the duration measurement procedure of the high-frequency energy radiation that we recently developed.