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2014.04.03 update
[Seismic and Tsunami data of the 2014 northern Chile Earthquake (Mw 8.2) observed by DONET(prompt report)]


Japan Agency for Marine-Earth Science and Technology (JAMSTEC) has been operating real-time seismic waves and tsunamis monitoring system at twenty ocean bottom stations with Dense Oceanfloor Network System for Earthquakes and Tsunamis (DONET) off the southeast coast of the Kii Peninsula, Japan, in addition to other three ocean bottom cabled systems off Kushiro-Tokachi in Hokkaido, Hatsushima in Sagami Bay, and Muroto Cape in Kochi. By using these ocean-bottom systems, we succeeded in real-time observation of seismic waves and tsunamis from Mw 8.2 earthquake occurred off the northern Chile on April 2 (Japan Standard Time).

Figure 1 shows the seismic waveforms observed by the ocean bottom seismometers at, from the top to the bottom, Kushiro cabled ocean bottom seismometer 1, KMA01 seismometer of DONET, and off-Muroto cabled seismometer 1, respectively. The P-wave (green area) arrived through the Earth’s core (= 2900 km depth) at 9:07 on April 2 (JST) about 20 minutes after the earthquake occurred. This was followed by the surface wave (blue area) around 9:56 which propagated along the Earth’s surface.

The tsunami followed by this earthquake reached Japan in the next morning. All ocean bottom pressure gauges of these systems observed tsunamis from 1cm to 2cm (Figure2). Amplitude of tsunamis has the property of being small in offshore and getting bigger as it approaches to coast. In the coastal areas, accordingly, it may become 10 times bigger, and amplified more depend on the coastal bathymetry. We could almost reproduce both arrival times and maximum amplitude of tsunami in a tsunami simulation that used a tsunami source model created by referring the information published by United States Geological Survey (USGS) (Figure3)

Figure 1. Seismic waveforms observed at Kushiro-Tokachi cabled seismometer 1, DONET, (KMA01) seismometer, and Muroto cabled seismometer 1, respectively.

Figure 2, Observed tsunami waveforms at, from the top to the bottom, all DONET stations (20 points), Kushiro-Tokachi cabled pressure gauges 1&2, Hatsushima cabled pressure gauge, and Muroto cabled pressure gauges 1&2.

Figure 3. From top to bottom, the theoretical tsunami waveforms at Kushiro-Tokachi cabled pressure gauge 1 (KPG1), DONET (KMC09) pressure gauge, and Muroto cabled pressure gauge 2 (MPG2).