An earthquake of magnitude 5.6 occurred on the island of Java, in Indonesia, on Monday November 21st at 07:21 AM Czech time (13:21 local time). Despite its moderate magnitude, the earthquake caused severe damage, claimed more than 40 casualties, and left several hundred people injured.
One reason for this high level of damage and number of deaths is the location of the earthquake: it occurred on the densely populated island of Java, only about 100 km southeast of the capital Jakarta, in the immediate vicinity of the town of Cianjur. Most earthquakes in the region occur on the plate boundary between the downgoing Indoaustralian Plate and the Sunda Plate, which is located south of the island of Java (see Figure). The chain of active volcanoes of the island of Java (visible in the topographic map) are another consequence of this configuration.
Today’s earthquake, however, occurred on a smaller fault onshore Java, which may exist because the convergence of the two plates is not perfectly perpendicular to the plate boundary.
Figure: Topographic map of the island of Java, showing past earthquakes (from the year 2000 to today) colored by their depths. The earthquake of Nov. 21, 2022, is shown with a green star.