An improved UK local magnitude scale from analysis of shear and lg-wave amplitudes

Booth, David. 2007 An improved UK local magnitude scale from analysis of shear and lg-wave amplitudes. Geophysical Journal International, 169. 593-601.

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The amplitudes of shear and Lg waves recorded at UK seismograph stations from local earthquakes in the range 0–600 km have been subjected to an analysis of variance, allowing separation of the effects of earthquake size, distance and station corrections for each recording site. The propagation paths sample mainly the central to western part of the UK, with good north–south coverage. The analysis of 385 amplitude readings at 28 stations from 40 earthquakes showed that the effects of both distance and station (site) corrections were statistically significant. Tables of corrections for both distance and station effects have been derived to allow local magnitude ML to be determined more accurately from horizontal and vertical component records. One set of tables allows the estimation of an ML which is consistent with the original Richter definition of ML, with a standard deviation which is smaller than that produced by the theoretical attenuation curve, defined according to attenuation in Southern California, which has customarily been used to calculate ML in the UK. The reduction in standard deviation is mainly due to the incorporation of station terms to correct for station effects, since the theoretical and observed variations of attenuation with distance are similar. This similarity implies that Southern California and the UK show a similar variation of distance-dependent attenuation for Lg waves, which was not expected in view of the differences in geology and tectonics. Another set of tables is provided to calculate an ML which is consistent with the body wave magnitude mb determined by the International Data Centre from station records of the Comprehensive Test-Ban Treaty Organization’s global monitoring network. The decay with distance of the predominantly Lg-wave amplitude values gives a value of 440 ± 50 for Lg Q at a frequency of 3 Hz, in agreement with estimates obtained from spectral displacement amplitudes of Lg waves in the UK.

Item Type: Publication - Article
Digital Object Identifier (DOI):
Programmes: BGS Programmes > Seismology and Geomagnetism
ISSN: 0956-540X
Additional Keywords: attenuation, statistical methods, surface waves, S waves
NORA Subject Terms: Earth Sciences
Date made live: 03 Jul 2007 10:25 +0 (UTC)

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