Noto-Hantou Earthquake

On January 1st, 2024 a magnitude 7.6 earthquake hit and struck Noto Peninsula (hantou in Japanese) of Ishikawa Prefecture, Japan. According to USGS the focal mechanism solutions for the earthquake indicate faulting occurred on a moderately dipping reverse fault striking to the southwest or northeast. 

This earthquake occurred on the west coast of Japan where crustal deformation created by the broader plate motions is accommodated in shallow faults. Shallow earthquakes cause more damage than intermediate- and deep-focus ones since the energy generated by the shallow events is released closer to the surface and therefore produces stronger shaking relative to earthquakes located deeper within the Earth. This coastal earthquake produced both strong shaking on land and generated a tsunami (USGS).

You can check the distribution of seismic intensity map produced by Japan Meteorological Agency here. You can also see the impact of the earthquake on the coastline areas analyzed by the Geospatial Information Authority of Japan from here.

In this post, I will add more information using very high spatial resolution of Planet data. Data before the earthquake was acquired on October 22, 2023, while data after the earthquake was acquired on January 2, 2024.

As you can see from the Figure below, the coastline was changed between ~150 to ~200 m. The land increasingly juts out into the sea, and in some location, there was uplift observed up to ~4 m (Geological Survey of Japan)

The blue line represents the coastline before the earthquake and the red line represents the coastline after the earthquake happened.

In some locations, I also observed small to large-scale landslides, as shown in the Figure below. Landslides occurred on steep slopes within the mountainous region. The landslide was represented in bright brown colour.

As shown in the Figure above, a large landslide was occurred and obscured the main road. The white colour in the Figure represents snow instead of cloud cover.

The RGB combination used to visualized the image is 642, while to extract the coastline I used the zero-crossing “edge detection” algorithm of GRASS within QGIS software. Regarding the method, I also assessed it using GEE, however, the result was not satisfactory, as shown the Figure below.

The red colour represents the coastline after the earthquake, and the yellow colour represents the coastline before the earthquake stroked.

Prior to zero-crossing “edge-detection” algorithm I transformed the multispectral data of Planet into NDVI and then create a binary mask. Then I apply the binary mask to the original NDVI image to get only land data.