9:00 AM - 9:15 AM
[HDS09-01] Rapid magnitude estimation using long-period components of seismic waves
Keywords:tsunami earthquake, magnitude
The Japan Meteorological Agency (JMA) usually uses estimations of hypocenter and magnitude for the tsunami forecast to issue tsunami warning as soon as possible. JMA-magnitude (MJ) that JMA estimates rapidly is almost the same as MW up to around 8 on average. However, when a magnitude is more than 8 such as the 2011 off the Pacific coast of Tohoku Earthquake, MJ is underestimated due to the saturation of amplitude-magnitude.
JMA uses several countermeasures for judging the MJ underestimation. The long-period components monitor of seismic waves is one of them, which is to monitor peak-amplitudes of composite displacements filtered with bandpass of 100s to 500s at broadband seismograph stations (JMA,2013). JMA can recognize that an earthquake has greater M from an empirical formula for the long-period components monitor, even if MJ is underestimated. The formula which was made using only the 2011 off the Pacific coast of Tohoku Earthquake and the Tokachi−oki Earthquake in 2003, is consist of a peak-amplitude and an epicentral distance.
We think that the long-period component monitor would be applicable also for detection of a tsunami earthquake which has the long source rupture duration because the pass band of 100s to 500s is long enough compared with the rupture durations of tsunami earthquakes.
We showed that MJ underestimated the size of tsunami earthquakes by 1 or more magnitude unit compared with MW (in Seismological Society Fall Meeting 2020). It can even be under 7. In this study we try to reconstruct an empirical formula for the long-period components monitor so as to adapt it to earthquakes in the latter of M6 and above. We will also show results in the case that the reconstructed formula is applied to tsunami earthquakes.
Acknowledgement: We used NIED F-net data.
JMA uses several countermeasures for judging the MJ underestimation. The long-period components monitor of seismic waves is one of them, which is to monitor peak-amplitudes of composite displacements filtered with bandpass of 100s to 500s at broadband seismograph stations (JMA,2013). JMA can recognize that an earthquake has greater M from an empirical formula for the long-period components monitor, even if MJ is underestimated. The formula which was made using only the 2011 off the Pacific coast of Tohoku Earthquake and the Tokachi−oki Earthquake in 2003, is consist of a peak-amplitude and an epicentral distance.
We think that the long-period component monitor would be applicable also for detection of a tsunami earthquake which has the long source rupture duration because the pass band of 100s to 500s is long enough compared with the rupture durations of tsunami earthquakes.
We showed that MJ underestimated the size of tsunami earthquakes by 1 or more magnitude unit compared with MW (in Seismological Society Fall Meeting 2020). It can even be under 7. In this study we try to reconstruct an empirical formula for the long-period components monitor so as to adapt it to earthquakes in the latter of M6 and above. We will also show results in the case that the reconstructed formula is applied to tsunami earthquakes.
Acknowledgement: We used NIED F-net data.