Abstract

By adapting and calibrating Bakun and Wentworth's (1997) solution strategy for seismic intensity observations for the Northern and Middle Rhine Area (NRA), Central Europe, local magnitudes with objective confidence-level uncertainties are estimated for 23 test-set earthquakes that occurred between 1692 and 1963. Analysis of 4375 Medvedev Sponheuer Karnik intensity (MSKI) observations for 14 instrumentally recorded and located training-set events suggests that an intensity magnitude, MLI, corresponding to local magnitude, ML, can be determined from the mean of MLIi = (MSKIi + 0.7374 + 0.0184 * Δi)/1.2673. Δi is the distance in km of observation MSKIi. In a grid of 81 × 51 trial epicenters, 5-km grid-point distance, contours of rms [MLI], where rms is the root mean square, bound the epicentral region. A total of 3628 intensity observations was used for the test-set earthquakes, seven of which showed MLI ≥ 5.5. The strongest historical events are the Verviers 1692 and the Düren 1756 events with MLI values of 6.8 and 6.4, respectively.

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