1 Ground Motion in SE Canada and the Central U.S. with Emphasis on Recent Earthquakes of 2008 Robert B. Herrmann Otto Nuttli Professor of Geophysics 2 Outline Earthquakes and mechanism Southeastern Canada Central United States April 18, 2008 S. Illinois Earthquake Thoughts 3 East vs West Well known, but now can compare on basis of similar Mw 200 km 400 km M5.4 Alum Rock, CA Oct 30, 2007 M5.2 Illinois, April 18, 2008 M5.4 Alum Rock, CA Oct 30, 2007 M5.2 Illinois, April 18, 2008 6 Two Eastern U.S. earthquakes 2002/04/40 10:50:44 UT Mw = 5.0 Au Sable, NY 2008/04/18 09:37:00 UT Mw=5.2 Mt. Carmel, IL 7 Intensity 8 Intensity vs Distance 9 Mechanism Thrust 45 degree dip slip H=10 km Strike slip H = 14 km 10 11 Focal Mechanisms for part of North America Why? more damage for Au Sable than Mt Carmel earthquake November 9, 1968 Mw=5.3 earthquake in southern Illinois, caused more damage in epicentral region, than did the Mt. Carmel earthquake however this was a 25 km deep thrust event, not a strike-slip; larger felt area 12 Source Mechanisms Mostly M > mechanisms since Raw waveforms available (red = 2008 earthquakes) 13 Orientation of maximum compressive stress axis. Style of faulting: red normal blue thrust green strike slip Note spatial patterns 14 Thoughts Source mechanism is important not just for stress drop but also for radiation pattern Significant variability at short distances Regional patterns of mechanism may require different ground motion scaling relations because of radiation pattern 15 SE Canada Ph.D. Dissertation Y. S. Jeon, SLU 390earthquakes 76 station channels 4500 observations Purpose Test Atkinson Boore 1995 scaling 16 17 Regression Peak filtered velocity, Fourier velocity A = E + D + S E : level of motion at 40 km D : distance (many nodes) S : Site Modeling stage 2 geometrical spreading, Q(f), kappa, etc For purposes here compare observed and predicted E for AB95 and A2004 models (note A2004 here only sigma=200 bars used) 18 AB95 19 A2004 20 AB95 21 A2004 22 AB95 vs A2004 Rather than focus on scaling with distance, compare predicted to observed where observed are well defined, e.g., 40 km 23 New Madrid Continuing effort 620earthquakes 360 station channels 12000 observations Purpose Define scaling Problems different networks, e.g., analog telemetry, PANDA, digital until April 18, largest EQ is Mw=4.2 24 25 Problems (cont) Wide variety of site conditions few hard rock sites Focus on amplitude vs distance Few calibrated events to use for source scaling test 26 NMD 27 AB95 28 Illinois Earthquake April 18, 2008 Largest since Mw= Mw= Mw= Mw= Mw=5.23 29 Illinois Earthquakes Mw=5.2, H= Mw=4.6, H= Mw=4.0, H= Mw=3.7, H=13 Same location, same depth, same mechanism data sets could be used to test scaling 30 31 WVIL 670 m/s; NEHRP C OLIL 945 m/s; NEHRP B USIN 705 m/s; NEHRP C EVIN 325 m/s; NEHRP D (our EVIN measurement site was located about 200 m southwest of the station) HAIL 765 m/s; NEHRP B ( W. Stephenson, R. Williams, J. Odum et al) (Bog Bauer of Ill. Geol Survey has others in IL) 32 Site characterization SSA Poster Presentation: Odum, J.K., Stephenson, W.J., Williams, R.A., and D.M. Worley, 2005, Examples of site characterization and Vs30 measurements at ANSS Stations at selected sites across the United States, Seism. Res. Lett., v. 76, no. 2, p Manuscript in Review: Odum, J.K, Williams, R.A. and Stephenson, W.J, Worley, D.M., 2008, Shallow Seismic Velocity and Vs30 at ANSS Sites in Southern Illinois and Evansville, Indiana Williams, R.A., Stephenson, W.J., Odum, J.K., and Worley, D.W., 2003, Seismic velocities from high-resolution surface-seismic imaging at six ANSS sites near Memphis, Tennessee: U.S. Geological Survey Open-File Report , 49 p. 33 High Frequency Ground Motion Broadbands 20, 40, 80, 100 Hz CMG3-ESP, STS-2 Accelerometers 50 Hz CMG5-TD 100 Hz Episensor Validate calibration STS-2 vs CMG5-TD at SLM CMG3-ESP vs Episensor at OLIL, USIN CMG3-ESP vs FBA3 at MPHECH.NA/ILLINOISEQ.REPORT 34 35 Q330 Accelerometer QC Observed/ Predicted Velocity 0.05 0.20 Hz 36 First view of peak ground motions Deconvolve all instruments to velocity in meters/sec (CMG-5TD good to 22 Hz because of FIR cutoff between Hz and noise Hz others flat response to 0.4 Nyquist Determine peak motion Differentiate to acceleration, determine peak Initial plots do not apply a S/N 37 Amax Vmax stations Do not have USNSN stations, CCM short period, NSMP sites. Interest was on new ANSS stations. 38 39 40 41 42 Summary There are differences in distance scaling SE Canada vs Central US at large distance related to crustal thickness at short distance to mechanism? note short distance requires good source depths, which are difficult except in a few locations 43 Source scaling is a problem Can test for Mw = 4 -> 5 No data for larger earthquakes Data sets only the Central U. S. and S. E. Canada have sufficient data sets for a detailed analysis, although New York may have some 44 Future Finalize analysis for data sets priority has been on determining Mw continent wide USNRC must provide long term support to capture significant earthquakes in detail and to learn as much as possible from small earthquakes 45 Network design must focus on USNRC needs high frequency scaling to large distance site effects continent wide scaling variation Cannot use Transportable Array (due in CUS in about 2 years) since only has 40 Hz sampling, no accelerometers 46 There are many interesting ground motion problems depending on application SH resonance in deep sediments kappa stress drop source scaling difficult high frequency ground motion scaling to large distance