Strong earthquake strikes western Japan, no tsunami riskーNHK WORLD-JAPAN NEWS

Key Concepts

• Magnitude: A measure of the energy released during an earthquake.
• Intensity (Japanese Scale - Shindo): A measure of the shaking felt at a specific location, ranging from 0 (not felt) to 7 (extremely strong).
• Long-Period Ground Motion (LPGM): Prolonged shaking, particularly affecting tall structures.
• Japan Meteorological Agency (JMA): The official agency responsible for monitoring and forecasting earthquakes and weather in Japan.
• Tsunami: A series of ocean waves caused by large-scale disturbances, such as underwater earthquakes.

Earthquake Events in Western Japan - January 23rd

This report details a series of strong earthquakes that impacted western Japan on Tuesday morning. Crucially, the Japan Meteorological Agency (JMA) has confirmed there is no tsunami threat associated with these events.

Initial Earthquake – Magnitude 6.2

The first earthquake occurred at 10:18 a.m. local time and registered a magnitude of 6.2 on the Richter scale. The epicenter was located in the prefectures of Totori and Shimane. The earthquake’s intensity, measured on the Japanese scale (Shindo) of 0 to 7, reached upper 5 in the areas experiencing the strongest shaking. An intensity of upper 5 indicates significant difficulty standing and potential for furniture to move.

Subsequent Earthquake – Magnitude 5.1

A second earthquake struck the same general area approximately ten minutes later, at 10:28 a.m. This event had a magnitude of 5.1. The intensity of this earthquake was recorded as lower 5 on the Shindo scale. Lower 5 signifies noticeable shaking, with some objects potentially falling.

Long-Period Ground Motion (LPGM)

The JMA has specifically noted the occurrence of long-period ground motion (LPGM) in both Totori and Shimane prefectures. This type of ground motion is characterized by prolonged shaking, and is particularly dangerous for tall buildings. The report highlights that LPGM can cause significant swaying in high-rise structures, especially on upper floors. This is due to the frequency of the shaking matching the natural frequency of these buildings, amplifying the motion.

Official Response & Future Updates

Officials from the Japan Meteorological Agency are preparing to hold a news conference to provide further details and updates on the situation. No specific details regarding damage or casualties were provided in this initial report.

Logical Connections

The report establishes a clear sequence of events: the initial 6.2 magnitude earthquake, followed by a 5.1 magnitude aftershock. The emphasis on the absence of a tsunami threat is a key piece of information, immediately addressing a primary concern following an earthquake. The specific mention of LPGM highlights a particular hazard associated with these earthquakes, beyond the immediate shaking.

Conclusion

The earthquakes in western Japan, while significant in magnitude and intensity, have not triggered a tsunami. The primary concern now focuses on the potential impact of long-period ground motion on tall buildings in Totori and Shimane prefectures. Further information is expected from the Japan Meteorological Agency’s upcoming press conference.