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A revised local magnitude scale for the UK

A revised local magnitude scale for the UK. Susanne Sargeant 1 and Lars Ottem ö ller 2 1 British Geological Survey, 2 University of Bergen ESC 2010 Montpellier. Outline. Background to this work Data and data processing Methodology UK North Sea.

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A revised local magnitude scale for the UK

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  1. A revised local magnitude scale for the UK Susanne Sargeant1 and Lars Ottemöller2 1 British Geological Survey, 2 University of Bergen ESC 2010 Montpellier

  2. Outline • Background to this work • Data and data processing • Methodology • UK • North Sea Seismicity of the UK and North Sea region, 1979-2009 (ML ≥ 2.5)

  3. Lg-wave attenuation ML distance correction Background Structure of the North Sea region (from Gautier, 2005)

  4. Aims • To determine a UK-specific local magnitude scale • To determine a local magnitude scale specifically for North Sea earthquakes using UK and Norwegian data

  5. Data and data processing • Simulate ground motions recorded on standard Wood-Anderson torsion seismograph (T=0.8 sec, magnification = 2080, damping = 0.8) • Events 2000-2010 • Only using data recorded within 1000 km • Minimum distance range • Map showing UK and Norwegian seismic networks

  6. Methodology Richter (1935): ML = log A – log A0 + S -log A0 = a log(r/100) + b(r-100) + 3.0

  7. Results for the UK

  8. Results for the UK Local magnitude scale for the UK is very similar to Southern California Station corrections normalised to ESK (model 1)

  9. North Sea

  10. Summary • The local magnitude scale determined using UK data is very similar to the scale determined for Southern California • A separate scale determined for North Sea earthquakes using data recorded in the UK and Norway indicates that.. • Including station corrections can reduce the standard deviation on the average magnitudes significantly.

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