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Local and regional distance earthquakes (0° - 15°)

Local and regional distance earthquakes (0° - 15°). 1. Introduction 2. Data examples 3. Exercises. Snells‘ Law for refracted waves: Sin i 1 /v p1 = sin i 2 /v p2 Critical angle (for P n waves): i 2 = 90°  sin i crit = v 1 /v 2 i crit = 48° for v 1 = 6 km/s and v 2 = 8 km/s

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Local and regional distance earthquakes (0° - 15°)

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  1. Local and regional distance earthquakes (0° - 15°) 1. Introduction 2. Data examples 3. Exercises

  2. Snells‘ Law for refracted waves: Sin i1/vp1 = sin i2/vp2 Critical angle (for Pn waves): i2 = 90°  sin icrit = v1/v2 icrit = 48° for v1= 6 km/s and v2= 8 km/s cross over distance xco between Pg and Pn: Rule of thumb: xco =5 zm zm = Moho depth e.g. zm = 30 km  xco = 150 km • Simplifications: • constant velocities, no gradients • first order disconinuity at Moho • flat Moho • no heterogeneities in crust vp1=6km/s vp2=8km/s

  3. Traveltime curves for crustal and uppermost mantle phases

  4. Local magnitude determination Richter magnitude ML (Richter, 1935) • originally developped for California • measured from standard Wood-Anderson horizontal component seismometer (natural period:Ts=0.8s, damping: Ds=0.8, amplification: Vmax=2800) • epicentral distance range: 0 – 500 km • restricted to sources in the crust ML = log Amax – log A0 Amax = zero-to-peak amplitude in mm A0 = amplitude-distance correction e.g. 1 mm at distance of 100km yield ML=3 Alternative: e.g. duration magnitude Md

  5. Exercises: • Event 1: 19-oct-2007 04:41 UTC • Event 2: 27-dec-2007 06:06 UTC • Event 3: 03-aug-2007 02:58 UTC • Event 4: 19-may-2007 16:19 UTC • Event 5: 27-feb-2008 05:22 UTC • Event 6: 27-jan-2008 11:10 UTC • Event 7: 23-feb-2008 15:30 UTC • Event 8: 18-jul-2009 02:39 UTC • Event 9: 28-oct-2008 10:55 UTC

  6. Results of exercises: • Event 1: 19-oct-2007, 04:41 UTC local event:Gera, lat: 50.80°, lon:12.13°, ML=3.8 • Event 2: 27-dec-2007, 06:06 UTC local event:Gera, lat: 50.80°, lon:12.13°, ML=1.5 • Event 3: 03-aug-2007, 02:58 UTC local event:Koblenz, lat: 50.37°, lon: 7.35°, ML=4.1 • Event 4: 19-may-2007, 16:19 UTC local event:Austria, lat: 47.13°, lon: 10.54°, ML=4.1 • Event 5: 27-feb-2008, 05:22 UTC mining event:W-Polen, lat: 51.46°, lon: 16.1°, ML=3.8, z=1km • Event 6: 27-jan-2008, 11:10 UTC local event:Klingenthal, lat: 50.22°, lon: 12.47°, ML=1.9 • Event 7: 23-feb-2008, 15:30 UTC mining event:Saarland, lat: 49.39°, lon: 6.85°, ML=4.2, z=1km • Event 8: 18-jul-2009, 02:39 UTC landslide:Nachterstedt, lat: 51.8°, lon: 11.40°, ML=1.7, z=0km • Event 9: 28-oct-2008, 10:55 UTC local events:Vogtland, lat: 50.22°, lon: 12.44°, ML=2.2, z=9km

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