One of the quickest means of tsunami evacuation is transfer to higher ground soon after strong and long ground shaking. Ground shaking itself is a good initiator of the evacuation from disastrous tsunami. Longer period seismic waves are considered to be more correlated with the earthquake magnitude. We investigated the possible application of this to tsunami hazard alarm using single-site ground motion observation. Information from the mass media is sometimes unavailable due to power failure soon after a large earthquake. Even when an official alarm is available, multiple information sources of tsunami alert would help people become aware of the coming risk of a tsunami. Thus, a device that indicates risk of a tsunami without requiring other data would be helpful to those who should evacuate. Since the sensitivity of a low-cost MEMS (microelectromechanical systems) accelerometer is sufficient for this purpose, tsunami alarm equipment for home use may be easily realized. Amplitude of long-period (20 s cutoff) displacement was proposed as the threshold for the alarm based on empirical relationships among magnitude, tsunami height, hypocentral distance, and peak ground displacement of seismic waves. Application of this method to recent major earthquakes indicated that such equipment could effectively alert people to the possibility of tsunami.
Early-stage tsunami warnings are usually issued by governmental
organizations, based on the estimated hypocenter and magnitude. Magnitude, a
crucial factor for tsunami forecasting, is estimated based on amplitude of
the seismic wave
If earthquake magnitude can be estimated using ground motion at a single site, residents can be alerted to evacuate before a potential tsunami. While strong ground motion indicates relatively large magnitude, it does not always mean tsunami hazard. Small, nearby earthquakes may have ground motion as strong as larger, more distant ones. Strong ground motion alone is therefore not a reliable indicator of tsunami hazard, so simply telling people to evacuate if they feel strong shaking is not enough. However, some people are reluctant to evacuate even after receiving an official tsunami warning. We feel that multiple independent warnings are much more compelling, provided the additional warnings are reasonably reliable. A stand-alone warning system would be valuable if the official warning were unavailable because of some mishap.
Low-cost MEMS (microelectromechanical systems) accelerometers could equip an
ordinary house with such a single-station tsunami alarm. Some single-site
processing methods have been proposed for earthquake early warning.
Examples of epicentral distance estimation using the method of
Table 1 lists earthquakes that involved 10 or more casualties due to
tsunamis around the Japanese islands in the past 100 years. This table
indicates that earthquakes with a magnitude of 8 (
Major disastrous earthquakes and casualties due to their tsunami around the Japanese islands in the past 100 years.
Numbers in parentheses indicate total casualties including those
due to causes other than tsunami.
We aim to distinguish events with tsunami potential from seismic data
obtained at a single station.
Station and epicenter map. Stations of seismic intensity meters (open circles) and epicenters of the events (solid circles) for which seismic records were used in this study are denoted.
For a 50 s cutoff, the value of
This method was applied to the data obtained with seismic intensity meters
installed by the
Data distribution of the maximum vertical displacement amplitude.
Amplitude data which exceed the threshold value (0.081 m) are presented by
red dots. The red line indicates the distance at which tsunami height is 2 m
based on the Eq. (
Figure
The false alarm due to large amplitude by a relatively small event is a problem in this method. Since the threshold of this study is a very rough estimation, false alarms are unavoidable. We tentatively checked other quantities such as peak ground velocity, duration of strong motion, and various combinations of these. No simple measure distinguished large earthquakes better than displacement amplitude.
The result is applied to several major earthquakes that occurred around Japan
and Chile. The same data used in the previous section are referenced in the
trials here for
events around Japan. Data archived
by the
Amplitude data distribution of the 2003 Tokachi-oki earthquake and the 2011 Great East Japan Earthquake. The dashed line indicates the threshold amplitude.
Map plot of the observational values for major earthquakes:
Seismic waves and instrumental seismic intensity obtained using prototype tsunami alarm equipment. Original acceleration records, velocity records for instrumental seismic intensity, instrumental seismic intensity, and displacement records are shown.
Regarding tsunami height, we referred to run-ups by
In Fig.
These examples illustrate that the single-station method is effective in indicating a high-risk area of a large tsunami in many areas and that it cannot cover the whole area of high tsunami. Even though this method does not cover a possible disastrous area completely, an alert based on this method may induce caution regarding the possibility of a tsunami after a large earthquake. Moreover, although threshold values were estimated with data obtained in Japan, these examples indicate that this method is applicable to earthquakes around Chile, which is located in a similar tectonic setting as Japan.
We built prototype tsunami alarm equipment using an MEMS sensor and a small
computer and tentatively observed ground motion with it. Records were
obtained for the 2015 Illapel earthquake at the site of 33.03
A 20 s cutoff is considered to be enough for ordinary earthquakes of
False alarms and missed warnings are unavoidable with this method, as shown in Sects. 3.1 and 3.2. There is a trade-off between the false alarms and missed warnings. If a message promoting confirmation of the official announcement is included in the alarm from the equipment, the problem of a false alert would be amended.
We proposed a method to differentiate earthquakes with disastrous tsunami potential from others using ground motion at a single site. With this method, displacement amplitude obtained with 20 s cutoff filter is used. It is possible to develop small equipment for this purpose using a low-cost MEMS sensor.
Application of this method to recent major earthquakes indicated that this method is partially effective in informing people of the possibility of a disastrous tsunami. Our sensors would not provide a perfect tsunami alarm system; instead, they would complement the official alarms. The priority should be placed on governmental information.
The number of casualties of the 2011 Great East Japan
Earthauke is available at
The authors declare that they have no conflict of interest.
We are grateful to the two anonymous referees and the editor, B. D. Malamud, for their kind and thoughtful comments. This study used strong motion data obtained by the Japan Meteorological Agency and the University of Chile. We referred to hypocenter locations estimated using the seismic data of the National Research Institute for Earth Science and Disaster Prevention, Hokkaido University, Hirosaki University, Tohoku University, the University of Tokyo, Nagoya University, Kyoto University, Kochi University, Kyushu University, Kagoshima University, the National Institute of Advanced Industrial Science and Technology, the Tokyo metropolitan government, the Shizuoka prefectural government, the Kanagawa prefectural government, the city of Yokohama, Japan Agency for Marine-Earth Science and Technology, and the Japan Meteorological Agency. This study was partly supported by the SATREPS research project of “Enhancement of technology to develop tsunami-resilient community”. Edited by: B. D. Malamud Reviewed by: two anonymous referees