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| Titel |
Lg-wave attenuation and earthquake source parameters in the UK |
| VerfasserIn |
S. Sargeant, L. Ottemoller |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250028089
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| Zusammenfassung |
| We investigated Lg-wave attenuation and earthquake sources in the UK with the purpose of
improving our understanding of ground motion in a region where there are few ground
motion data of engineering significance. The regional average Lg-wave quality factor (QLg)
in Britain was determined using data from the UK seismic network (Q(f) = 266f0.53
between 1 and 10 Hz). The dataset used to constrain the model consists of vertical,
mostly short-period recordings of 64 earthquakes in the magnitude range 2.7-4.7
ML recorded between January 1984 and April 2007. Using this model, seismic
moment, stress drop and rupture radius are determined from vertical shear-wave
displacement spectra for these earthquakes using a grid search method. Source
parameters for three of the largest British earthquakes that have occurred during the
instrumental period are also determined from a limited number of on-scale records. These
are Lleyn Peninsula (19 July 1984, 5.4 ML), Bishop’s Castle (2 April 1990, 5.1
ML) and Lincolnshire (27 February 2008, 5.2 ML). Moment magnitudes for the
whole dataset (i.e. 2.7-5.4 ML) range from 2.5-4.8 Mw. These values are consistent
with estimates made using a quadratic relation for converting ML to Mw that was
determined for north-west Europe (Grünthal and Wahlström, 2003). Stress drops lie in the
range 1-250 bars. In general, this parameter is poorly constrained because of the
uncertainty in the near-surface attenuation and no attempt has been made to characterise
near-surface attenuation in the modelling. The median stress drop for the dataset is
relatively low (c. 15 bars). The highest stress drop (250 bars ±87) is associated
with the 2008 Lincolnshire earthquake. This appears to be a relatively unusual
event within the context of UK seismicity. The next highest stress drop is just over
100 bars. Stress drop does not appear to be magnitude-dependent but does seem to
increase with depth. The results are used to model ground motion for key events. |
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