Germany, Buttlar: 1975-2018

The Buttlar cluster is named for a nearby municipality in the state of Hesse in central Germany. The cluster is based on two moderate-sized earthquakes that occurred on June 23, 1975 (mb 5.5) and March 13, 1989 (mb 5.4). The cluster is small, only 17 events, and none of the other events is larger than 3.8 mb or recorded beyond about 500-600 km. Calibration of the epicenters is very robust but depth constraint is difficult because all events appear to be very shallow. One event is clearly associated with a mining facility and has been set to zero depth (local elevation is ~600 m). The depth of the mb 5.4 event in 1989 is constrained to 6 km by a station extremely near to the event, but there is no depth constraint for the mb 5.5 event [...]