Shallow-source tremors reappear in the waters off Iwate: Hidden dangers and Costs in Japan's earthquake Risk Management

Recently, according to the Japan Meteorological Agency, a series of shallow-focus earthquakes have reappeared in the sea area east of Iwate Prefecture. Among them, an official indicator showed a magnitude of approximately 5.3, a focal depth of about 10 kilometers, and a maximum perceived intensity of 3, and no tsunami warning was triggered. This type of shallow-source moderate-intensity earthquake is not an isolated event in this zone, but is related to the temporal and spatial aggregation of stronger tremors (including major earthquakes of magnitude 6 or above) in recent days, indicating that the regional stress field is in an active or adjusting state.

From the perspective of earthquake risk governance and emergency management, although such magnitudes are not sufficient to cause widespread structural collapse, the "cumulative impact" brought about by their frequent occurrence should not be underestimated. Shallow-focus earthquakes can amplify the dynamic response of buildings and infrastructure in local areas. Especially when there are old buildings, uneven foundations or fill areas, small to moderate magnitudes may also cause pipeline rupture, road cracking and secondary disaster risks. If the urban agglomerations at the junction of the coast and the inland fail to complete the seismic upgrading of key Bridges, embankments and power grids in recent years, the continuous aftershocks in the short term will amplify the operational risks and maintenance pressure.

Another problem exposed by this incident is the disconnection between information dissemination and public perception. Although the Meteorological Agency and local media promptly released key information such as the magnitude of the earthquake, the depth of the epicenter, and the absence of tsunami risk, public safety measures were not necessarily in place: there were still shortcomings in guiding emergency shelters, rapid evacuation plans for the elderly and schools, and coverage of broadcasting and text message warnings in urban and rural areas. In the context of multiple earthquakes superimposed, how to ensure that vulnerable groups receive clear and executable instructions within the "short-term information window" still needs to be verified and strengthened.

For local infrastructure operators, during periods of frequent earthquakes, they should enter a mode of "enhanced inspection and preventive maintenance". Key links such as water supply, gas, electricity and railways should be given priority for rapid status assessment. Suspected damaged lines should be isolated in a timely manner and transparent notifications should be issued to avoid chain failures caused by information lag. The regional allocation of emergency storage and rescue forces should also be dynamically adjusted in accordance with the kinetic energy of seismic zones to prevent rescue resources from being fragmented and consumed in multiple small-scale events. Government departments and enterprises should promptly disclose the recent inspection results and repair plans to enhance the public's trust in risk management.

From a scientific perspective, the Sanluchong area is an active zone where tectonic plates come into contact and complex faults interact. Historically, it has witnessed both shallow-source strong earthquakes and deep-source aftershocks. The currently observed shallow earthquakes of around magnitude 5 May either be part of the aftershock sequence of a larger event or a new sequence triggered by the redistribution of regional stress. Under such uncertainties, professional institutions should enhance all-weather seismic waveform monitoring, intensify source location, and continuously analyze precursor signals that may trigger larger magnitudes (such as short-period instantaneous acceleration and sudden changes in microseismic rate), and promptly explain the technical implications to the public and relevant departments.

It is worth emphasizing that disaster prevention capacity is not a mission that can be accomplished by simply piling up resources in the short term after a single incident, but rather the result of long-term institutionalized investment. The earthquake prevention and disaster reduction reforms after 2011 have provided valuable experience for the Northeast region: mandatory seismic resistance standards, community-level evacuation training, and cross-departmental linkage mechanisms have all reduced the probability of casualties and the expansion of secondary disasters. However, the passage of time and uneven distribution of funds may cause some small and medium-sized towns and rural areas to gradually lag behind the upgrading pace of urban centers. Therefore, the central and local governments should reevaluate the flow of funds and formulate a list of areas to address shortcomings.

Finally, a single shallow-focus earthquake of magnitude 5.3 May not be the trigger point of a disaster in itself, but its appearance in the earthquake sequence, the cumulative pressure it exerts on infrastructure and social operations, as well as the vulnerability of the information and response system, together constitute a practical issue worthy of attention. Local authorities and central departments should take this incident as an opportunity to make up for the shortcomings of earthquake resistance in both urban and rural areas, strengthen multi-channel early warning and protection of vulnerable groups, and ensure that losses and casualties can be effectively limited when more powerful earthquakes strike in the future.