Japan Geoscience Union Meeting 2019

Presentation information

[J] Poster

H (Human Geosciences ) » H-DS Disaster geosciences

[H-DS13] Tsunami and Tsunami Forecast

Tue. May 28, 2019 1:45 PM - 3:15 PM Poster Hall (International Exhibition Hall8, Makuhari Messe)

convener:Naotaka YAMAMOTO CHIKASADA(National Research Institute for Earth Science and Disaster Resilience), Hiroaki Tsushima(Japan Meteorological Agency), Tatsuya Kubota(National Research Institute for Earth Science and Disaster Resilience)

[HDS13-P09] Estimation of local seismic waves and rapid magnitudes for ‘slow tsunami earthquakes’ based on moment rate spectrum

*Takahito Nishimiya1, Akio Katsumata1 (1.Meteorological Research Institute, Japan Meteorological Agency)

Keywords:tsunami earthquake, spectrum, local seismic wave, magnitude

The tsunami height estimation at earliest stage in JMA is based on the estimated hypocenter and rapid magnitude (rapid-M) from local seismic wave data. The amplitudes of seismic waves from ‘slow tsunami earthquakes’ are usually smaller than those from normal earthquakes because those earthquakes radiate relatively low seismic energies in the short period range. Therefore it is difficult to estimate rapid-M of ‘slow tsunami earthquakes’ accurately. We would like to evaluate rapid-M of them quantitatively. However local seismic wave data of slow tsunami earthquakes is almost not available.

We estimated moment rate spectra of ‘slow tsunami earthquakes’ using tele-seismic wave data (in JpGU Meeting 2018), and calculated synthetic local seismic waves based on those spectra (in Seismological Society Fall Meeting 2018). We estimated rapid-M from the synthetic wave data here.

JMA magnitude (MJ) and M100 (Katsumata et al., 2013) are evaluated as the rapid-M. M100 is introduced by JMA to avoid underestimation of magnitude for huge earthquakes because MJ tends to indicate “magnitude saturation” for huge earthquakes. We calculated MJ and M100 from the synthetic wave data. REGARD (Kawamoto, 2017) based on GNSS data is also a kind of rapid-M. However we use seismic wave data from which smaller magnitude can be estimated compared with REGARD.

We assumed that a ‘slow tsunami earthquake’ occurs at the plate-boundary off the Pacific coast of Tohoku. It has the same moment rate spectrum as the Java tsunami earthquake (Mw7.8) in 1994. MJ estimated from those synthetic waves was smaller than Mw by more than 1.0. M100 is larger than MJ, but M100 is smaller than Mw by more than 0.5. We also evaluated magnitudes for an earthquake which has the same moment rate spectrum as the Sumatera tsunami earthquake (Mw7.8) in 2010. The difference from Mw reduced for the earthquake, while both MJ and M100 are lower than Mw.
USGS published Ms of significant earthquakes. Ms of the 1994 Java earthquake was lower than Mw by more than 0.5 although Ms of the 2010 Sumatera earthquake was about the same as Mw.

Our results suggest that big difference between M100 and MJ is useful for early discriminating ‘slow tsunami earthquakes’ from normal earthquakes. Even if M100 is much greater than MJ, M100 may be underestimated for slow tsunami earthquakes.