Publication Date:
2011-12-01
Description:
We estimate moment magnitudes M (sub w) for earthquakes in Switzerland recorded between 1998 and 2009 using three different spectral methods. The M (sub w) estimation in Switzerland is extended to lower magnitudes (local magnitude M (sub L) 0.1), and scaling relations between M (sub L) and M (sub w) are investigated. Above M (sub L) 4, the obtained M (sub w) estimates are consistent with the previously obtained scaling relation of M (sub w) =M (sub L) -0.3 at the Swiss Seismological Service (SED). Below M (sub L) 4, all three methods indicate that a 1:1-type relationship is inappropriate. Therefore, we propose a new piecewise empirical scaling relation for earthquakes in Switzerland. The scaling is linear below M (sub L) 2 and above M (sub L) 4. To obtain a smooth transition between the two linear scales we fit a quadratic relation in between (2〈 or =M (sub L) 〈 or =4). This scaling relation is also consistent with M (sub w) estimates from moment-tensor (MT) solutions based on broadband waveform fitting of local earthquakes with M (sub L) 〉3.0. We have tested all three methods carefully to ensure that the observed break in scale at around M 3 cannot be attributed to bias in the M (sub w) determination. However, we cannot determine with certainty from the dataset at hand whether the break in scaling is due to bias in the routine determination of M (sub L) or to physical properties of the source.
Print ISSN:
0037-1106
Electronic ISSN:
1943-3573
Topics:
Geosciences
,
Physics
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