Magnitude, intensity and displacement tell different parts of an earthquake
A shallow magnitude 6.8 earthquake in Kyushu reached Shindo 7 intensity, while Sentinel-1 measured 65 cm of uplift after Venezuela's rupture. Different scales separate hazard from ground motion.
Science··Morning
The intensity of a shallow focus in Kyushu
The earthquake south of Kumamoto occurred on a strike-slip fault at about 10 km depth and magnitude 6.8. Shaking reached Shindo 7, the top step of Japan's local intensity scale; roads and buildings were damaged and fires broke out. Two tectonic regimes meet there: the Philippine Sea Plate subducts beneath the Eurasian Plate at 40–50 mm per year while back-arc rifting opens the Beppu-Shimabara graben. The shallow focus helps explain the high intensity at the surface.[1]
The surface measured by radar in Venezuela
After Venezuela's twin earthquakes of 24 June, Copernicus Sentinel-1 measured 65 cm of upward displacement around Caracas, La Guaira and Caraballeda. The second shock had magnitude 7.5. C-band radar interferometry compares passes from 18 June and 24–25 June; the first assessment had indicated about 30 cm. The images place most of the rupture offshore. Eight years of monitoring had shown the western fault section locked and accumulating 15 mm per year of plate motion.[2]
One event class, different questions
Magnitude describes energy released at the source; intensity scales such as Shindo describe shaking experienced at a particular place; radar interferometry describes surface change between satellite passes. The Kyushu report foregrounds how a shallow earthquake is felt in settlements. The Venezuela measurement maps where rupture produced lasting displacement and by how much. The numbers are not interchangeable: emergency response needs intensity and damage, while fault analysis needs the spatial pattern of displacement.[1], [2]
