Investigation of the North America Earthquake Process

1. Rober B. Herrmann Saint Louis University Investigation of the North America Earthquake Process

2. Motivation Seismic Networks Ground Motion Moment Tensor Crustal Model

3. Source Inversion • Requires Earth model • Codes • Calibrated instruments • Crustal Model • Surface-wave dispersion • Receiver functions • Tomography • High frequency Ground Motion • Networks • Regression • Calibration

4. Presentation • Moment Tensor Inversion • Crustal Model Selection • An interesting earthquake • source inversion • local low frequency site effects • testing high frequency ground motion models

5. Source Studies • Look at all M > 3.5 earthquakes in North America, except • California • California Integrated Network has sufficient stations and automatic procedure • Offshore events • Limited by 1-D models for synthetics • Deep Alaska events • Do not have synthetics for deep events • In support of PAGER of USGS

6. Objective • Use documented processing • Define procedure for conversion to Java for NEIC Hydra • Improve efficiency • Reduce possibility of improper use by analyst

7. Setup Event Processing(could be generated by location program)‏

8. #!/bin/sh ##### # valid regions # REG Region FELTID VELOCITY_MODEL # HI Hawaii hi [Not implemented June 23, 2007] # AK Alaska ak CUS (in continent from Rockies -no deep)‏ # CA California ca WUS # PNW Pacific Northwestrn pnw WUS # IMW Intermountain west imw WUS # CUS Central US cus CUS # NE Northeastern US ne CUS # ECAN Eastern Canada ous CUS (in continent from Rockies)‏ # WCAN Western Canada ous [Not implemented June 23, 2007] ##### # Command syntax: #DOCWBREG YEAR MO DY HR MN SC MSC LAT LON DEP MAG REG NEIC FELTID STATE/COUNTRY ##### DOCWBREG "2008" "06" "04" "14" "02" "43" "000" " 36.5130" " -106.3550" " 5.0" \ " 3.70" "CUS" "swba" "X2008swba" "New Mexico"

9. DOCWBREG • DOSETUP • create directory structure • copy all scripts for model and point to precomputed Green's functions • DOQUERY • use USGS CWBQuery.jar to get waveforms from USGS Continuous Wave Buffer • deconvolve perform QC • DOSOLUTION • get moment tensor and create documentation

10. Can create DOWILBURII • CWBQuery gets waveforms and responses from Continous Wave Buffer • USGS also wrote • mdget – to get metadata from dataless SEED • synget – to get Green's functions or make synthetics from Green's functions

11. query -t sac -o \"%N.SAC\" -sacpz nm -b '"'2008/06/17\ 11:44:00'"' -d 30 -s \".......BHZ..\" • Networks • AK, AT, AU, AV, BK, CH, CI, CN, CU, CZ, G, GE, GT, HV, IC, II, IM, IU, IW, JP, KN, KZ, LB, LD, LI, MN, MY, NE, NM, NN, PL, PM, PR, PT, TA, TW, UO, US, UW, XX

12. Data Preparation • Deconvolve to ground velocity (m/s) in 0.005 – 0.25 fN Hz band • Rotate to Vertical, Radial, Transverse • Decimate for surface-wave studies • Select stations Distance < 600 km • Perform QC • gsac command • ppk qc perplot 3 • look for S on transverse before Z or R

13. ppk qc perplot 3 – view filtered traces – test filter selection copy to inversion arena

14. DOSOLUTION • Grid search • Comparison graphics • DOHTML to create web page

25. Detailed Documentation • Not many earthquake annually • 2006 – 26 earthquakes • 2007 – 31 earthquakes • 2008 – 41 earthquake through 17/06/2008 • Document interesting waveforms • Preserve accessible data sets of significant earthquakes for other research (e.g.,Ms(VMAX)‏

26. Results – Part I • Moment tensors • 260 earthquakes in catalog (245 done at SLU)‏ • patterns of direction of maximum compressive stress • patterns of typical faulting

27. 261 Eqs

28. Maximum compressive stress - Green - SS Red - Normal Blue - Thrust

29. 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

30. Results – Part II • Use of inversion results for magnitude scale calibration Ms(VMAX) of Russell and Bonner (2007)‏

31. Ms(VMAX)‏ Russell and Bonner

35. Value of Ms(VMAX)‏ • Simple processing • set of narrow bandpass Butterworth filters • application of simple equation • Can be used for rapid 1st order estimate of Mw before a moment tensor can be obtained • Can be used regionally • Mechanism dependent adjustments

36. Illinois Earthquake April 18, 2008 • Largest since 1968 • 19681108 Mw=5.29 • 19740403 Mw=4.35 • 19870610 Mw=4.55 • 20020618 Mw=4.55 • 20080418 Mw=5.23

37. Illinois Earthquakes 20080418093700 Mw=5.2, H=14 20080418151416 Mw=4.6, H=14 20080421053830 Mw=4.0, H=15 20080425173100 Mw=3.7, H=13 Same location, same depth, same mechanism data sets could be used to test scaling

39. 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)‏

40. 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 MPH www.eas.slu.edu/Earthquake_Center/MECH.NA/ILLINOISEQ.REPORT

42. Q330 Accelerometer QCObserved/ Predicted Velocity 0.05 – 0.20 Hz

43. Amax Vmax stations Do not have USNSN stations, CCM short period, NSMP sites. Interest was on new ANSS stations.

48. Results – Part III • Detailed source studies

49. Summary • Systematic and documented inversion provides basic information for • earthquake • catalogs • ML calibration • understanding of tectonic process • Easy now and very easy for most of North America with simple structure