Investigation of the North America Earthquake Process Rober

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

Motivation Seismic Networks Ground Motion Moment Tensor Crustal Model 2

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

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

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 5

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

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

#!/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" "X 2008 swba" "New Mexico" 8

• 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 9

• 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 10

• 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 11

Data Preparation • Deconvolve to ground velocity (m/s) in 0. 005 – 0. 25 f. N 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 12

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

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

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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) 25

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

261 Eqs 27

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

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 29

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

Ms(VMAX) Russell and Bonner 31

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

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 36

Illinois Earthquakes 20080418093700 Mw=5. 2, H=14 20080421053830 Mw=4. 0, H=15 20080418151416 Mw=4. 6, H=14 20080425173100 Mw=3. 7, H=13 Same location, same depth, same mechanism data sets could be used to test scaling 37

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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) 39

High Frequency Ground Motion • Broadbands – 20, 40, 80, 100 Hz CMG 3 -ESP, STS-2 • Accelerometers – 50 Hz CMG 5 -TD – 100 Hz Episensor • Validate calibration – STS-2 vs CMG 5 -TD at SLM – CMG 3 -ESP vs Episensor at OLIL, USIN – CMG 3 -ESP vs FBA 3 at MPH www. eas. slu. edu/Earthquake_Center/M ECH. NA/ILLINOISEQ. REPORT 40

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Q 330 Accelerometer QC Observed/ Predicted Velocity 0. 05 – 0. 20 Hz 42

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

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Results – Part III • Detailed source studies 48

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 49