Exploring recent earthquake activity and seismic hazard patterns around Japan.
Japan experiences thousands of earthquakes per year, and many additional tremors that go unfelt. Earthquakes are frequent in the area because Japan is located at the intersection of several tectonic plates:
- Amur
- Okinawa
- Okhotsk
- Pacific
- Philippine Sea
- Yangtze
Real-time maps (such as the USGS Latest Earthquakes) show where earthquakes have recently occurred; hazard maps outline where strong shaking is more likely to occur; fault traces and plate boundaries explain the underlying mechanics; and population models reveal where people live in relation to these forces. Viewed separately, each dataset tells only part of the story. Seen together, they offer a clearer sense of how seismic activity, geological structure, and human settlement overlap.
This work brings those threads together in a single place so it’s easier to explore questions such as:
- Where earthquakes have occurred recently
- How those events align with major faults and plate boundaries
- How long-term shaking forecasts compare with the current pattern of seismicity
- How population is distributed relative to areas with higher probabilities of strong shaking
This project is exploratory rather than predictive or analytical. The maps were designed for general users interested in navigating Japan’s seismic landscape without requiring specialized technical knowledge.
Study area
The study area covers Japan and surrounding offshore regions:
- The four main islands (Hokkaido, Honshu, Shikoku, Kyushu) and nearby smaller islands
- Adjacent offshore areas where earthquakes occur along major plate boundaries
The map extent of the apps is constrained so users stay focused on Japan instead of panning off into the rest of the world.
Data sources
This project used a combination of open data services from the USGS and ArcGIS Living Atlas, plus authoritative Japanese sources for interpretation.
| Layer | Dataset / service | Usage |
|---|---|---|
| Recent earthquakes | Recent Earthquakes | Filtered to earthquakes within the map extent, with magnitude and time window controlled by the app’s widgets. |
| Active faults | Global Active Earthquake Faults | Provides generalized fault locations for reference against recent earthquakes. |
| Seismic motion forecast | 確率論的地震動予測地図 最大ケース | Map image layer showing the probability that a location will experience strong shaking over a 30-year period. |
| Population 100m | WorldPop Total Population 2000-2020 100m | Shows estimated total population per 100-meter cell, used in the population vs hazard swipe map. |
| Prefecture boundaries | 平成 27 年国勢調査 都道府県界 – Japan Prefecture Boundaries ECM | Administrative context for where earthquakes and hazards occur. |
| Tectonic Plates and Boundaries | Tectonic Plates and Boundaries | Shows plate boundaries and major plate polygons around Japan. |
Recent earthquake explorer
This web app focuses on recent earthquake activity in and around Japan. It uses a time filter, spatial filter, and attribute filters to highlight earthquakes that are relevant to the study area.
Navigating the map
Explore the map → Pan and zoom to different regions of Japan. Use the mouse scroll wheel or the zoom buttons to change scale.
Filter by time → Use the time slider to adjust the start and end dates of the earthquake window. Watch the earthquake symbols and the stats panel update as you move through time.
Filter by magnitude → Adjust the minimum magnitude slider to show only stronger earthquakes. As you move the slider, the map and the summary stats update.
Inspect individual events → Click any earthquake point to open a pop-up with location, depth, magnitude, and tsunami warning status.
Population vs seismic motion forecast
The second web app uses a swipe tool to compare total population on the left and probabilistic seismic motion forecast on the right.
The seismic motion forecast layer (published by Japan’s J-SHIS) may take a while to load, especially on slower connections.
This map lets users visually answer questions like:
- Where do higher population densities overlap with higher probabilities of strong shaking?
- Which coastal or urban regions stand out as both heavily populated and seismically exposed?
Navigating the map
Explore the map → Pan and zoom around Japan to focus on particular regions (e.g., Tokyo, Osaka, or coastal Tohoku).
Use the swipe handle → Drag the vertical swipe bar left and right. The left side shows estimated total population per 100-m cell (WorldPop). The right side shows the probability of strong shaking (JMA 6-lower or higher) between 2023 and 2052.
Think in terms of exposure, not risk → This app does not model vulnerability, preparedness, or secondary hazards like tsunami or fire. It simply helps users see where many people live in areas with higher probabilities of strong shaking.
JMA seismic intensity scale
Unlike magnitude (which measures total energy released during an earthquake event), JMA seismic intensity describes how strongly the shaking is felt at a particular location. The JMA scale has 10 levels, described by the Japan Meteorological Agency in the following illustration.
The seismic motion forecast layer used in the web app focuses on the probability that a location will experience JMA intensity 6-lower or stronger over a 30-year period (2023–2052).
Summary
Building these web apps highlighted a few key lessons:
Performance vs. detail is a trade-off. The high-resolution population rasters and large earthquake catalogs are both heavy. I had to balance detail with responsiveness, especially when setting default map extents, time windows, and visibility ranges.
Symbology and language matter. The seismic motion forecast layer is only available in Japanese, and includes a specialized legend. Building the apps via the SDK allowed me to override the legend labels with translated, simplified descriptions (e.g., “Up to 20% chance”) to make the map usable for English reading audiences.
Earthquake “risk” is not the same as “hazard.” The apps visualize where earthquakes have occurred and where shaking is more likely, but they do not account for infrastructure resilience or preparedness. It was important to be explicit that this project is exploratory, not a formal risk analysis.
JavaScript API + web components are powerful. Working with the ArcGIS Maps SDK for JavaScript and the web components gave me a lot of control over layout and interaction, but also required careful attention to layer ordering, scale visibility, and widget behavior. It was a fun challenge.