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J. Louie UNR Geol492/692 Spring 2005 Using Refraction Microtremor reconnaissance:  Rapid surveys take advantage of urban noise  More details at www.seismo.unr.edu/hazsurv.

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Presentation on theme: "J. Louie UNR Geol492/692 Spring 2005 Using Refraction Microtremor reconnaissance:  Rapid surveys take advantage of urban noise  More details at www.seismo.unr.edu/hazsurv."— Presentation transcript:

1 J. Louie UNR Geol492/692 Spring 2005 Using Refraction Microtremor reconnaissance:  Rapid surveys take advantage of urban noise  More details at www.seismo.unr.edu/hazsurv Surveying Seismic Microzonation in Urban Areas

2 J. Louie UNR Geol492/692 Spring 2005 Surface waves show different velocities at different frequencies– but only after some distance. Refraction Microtremor for Shallow Shear Velocity Initial funding from SCEC, UNR, VUW, Optim LLC Raw Data >14 Hz Filter <4 Hz Filter

3 J. Louie UNR Geol492/692 Spring 2005 ReMi measures Rayleigh dispersion with linear refraction arrays (paper by Louie, April 2001 BSSA). Refraction Microtremor for Shallow Shear Velocity Initial funding from SCEC, UNR, VUW, Optim LLC The array has to have at least 12 channels; 150 m length; and recorded for 4 sec (for 30-m depth resolution and 1-Hz frequency resolution).

4 J. Louie UNR Geol492/692 Spring 2005 City traffic gives appropriate 4-16 Hz signal. Refraction Microtremor for Shallow Shear Velocity Initial funding from SCEC, UNR, VUW, Optim LLC

5 J. Louie UNR Geol492/692 Spring 2005 A wavefield transform from (x, t)-space to (p, f)- space shows phase-velocity dispersion (McMechan and Yedlin, 1981). Refraction Microtremor for Shallow Shear Velocity Initial funding from SCEC, UNR, VUW, Optim LLC

6 J. Louie UNR Geol492/692 Spring 2005 What if energy arrives transverse to the linear array? Refraction Microtremor for Shallow Shear Velocity Initial funding from SCEC, UNR, VUW, Optim LLC

7 J. Louie UNR Geol492/692 Spring 2005 What if energy arrives transverse to the linear array? Refraction Microtremor for Shallow Shear Velocity Initial funding from SCEC, UNR, VUW, Optim LLC

8 J. Louie UNR Geol492/692 Spring 2005 What is our low-frequency detection limit? Can we use standard 4-16 Hz geophones that are easy to deploy? Cluster-test microtremor records show we get data down to 25-50% of the geophone frequency! Refraction Microtremor for Shallow Shear Velocity Initial funding from SCEC, UNR, VUW, Optim LLC

9 J. Louie UNR Geol492/692 Spring 2005 The minimum-velocity envelope represents the Rayleigh fundamental-mode dispersion curve. Kinematic data only, that we model for a shear- velocity versus depth profile. Refraction Microtremor for Shallow Shear Velocity Initial funding from SCEC, UNR, VUW, Optim LLC

10 J. Louie UNR Geol492/692 Spring 2005 We don’t invert for Vs(z), we forward-model interactively by hand. Refraction Microtremor for Shallow Shear Velocity 100-m depth resolution Initial funding from SCEC, UNR, VUW, Optim LLC

11 J. Louie UNR Geol492/692 Spring 2005 Fieldwork is quick and simple; best results in cities. Refraction Microtremor for Shallow Shear Velocity Initial funding from SCEC, UNR, VUW, Optim LLC

12 J. Louie UNR Geol492/692 Spring 2005 Fieldwork is quick and simple; best results in cities. Refraction Microtremor for Shallow Shear Velocity Initial funding from SCEC, UNR, VUW, Optim LLC

13 J. Louie UNR Geol492/692 Spring 2005 Low-frequencies, 1-20 Hz, so bad geophone plants still work. Refraction Microtremor for Shallow Shear Velocity Initial funding from SCEC, UNR, VUW, Optim LLC

14 J. Louie UNR Geol492/692 Spring 2005 Low-frequencies, 1-20 Hz, so bad geophone plants still work. Refraction Microtremor for Shallow Shear Velocity Initial funding from SCEC, UNR, VUW, Optim LLC

15 J. Louie UNR Geol492/692 Spring 2005 Fieldwork is quick and simple; best results in cities. Refraction Microtremor for Shallow Shear Velocity Initial funding from SCEC, UNR, VUW, Optim LLC

16 J. Louie UNR Geol492/692 Spring 2005 Fieldwork is quick and simple; best results in cities. Refraction Microtremor for Shallow Shear Velocity Initial funding from SCEC, UNR, VUW, Optim LLC

17 J. Louie UNR Geol492/692 Spring 2005 Fieldwork is quick and simple; best results in cities. Refraction Microtremor for Shallow Shear Velocity Initial funding from SCEC, UNR, VUW, Optim LLC

18 J. Louie UNR Geol492/692 Spring 2005 ReMi has classified hard and soft sites around the world by measuring V 30, average shear velocity to 30 m depth. Refraction Microtremor for Shallow Shear Velocity

19 J. Louie UNR Geol492/692 Spring 2005 Local reconnaissance was first large-scale test. Reno Transect Supported by UNR and IRIS-PASSCAL

20 J. Louie UNR Geol492/692 Spring 2005 Unexpected results: high V 30 in active alluvium. Reno Transect WestEast Ta

21 J. Louie UNR Geol492/692 Spring 2005 Transect has results to 300 m depth, shown here to 500 m. V 30 is only the shallow part that the IBC2000 requires measuring. Reno Transect

22 J. Louie UNR Geol492/692 Spring 2005 Lack of V 30 correlation to geologic or soil maps. Only Tertiary Andesite (Ta) shows a characteristic V 30. Reno Transect

23 J. Louie UNR Geol492/692 Spring 2005 Lack of V 30 correlation to geologic or soil maps Reno Transect

24 J. Louie UNR Geol492/692 Spring 2005 Basin info from 2000 gravity work. Reno Transect

25 J. Louie UNR Geol492/692 Spring 2005 Most of basin fill is Tertiary. Reno Transect

26 J. Louie UNR Geol492/692 Spring 2005 The First Reno Hazard Map

27 J. Louie UNR Geol492/692 Spring 2005 We Follow Field’s (2001) Amplification-Mapping Strategy

28 J. Louie UNR Geol492/692 Spring 2005 July 2003 San Gabriel Valley & Los Angeles Shallow Shear-Velocity Transects B C D E Transect mapped on NEHRP hazard class map by Wills, from SCEC Phase 3 Report Supported by USGS, NEHRP ERP and IRIS-PASSCAL

29 J. Louie UNR Geol492/692 Spring 2005 Los Angeles Transect  Approximately 60 km in length  Followed San Gabriel River Bike Path  20 m takeout interval, 300 m array, recorded for 30 min  4 teams, 3 people each, 4.5 days  120 IRIS/PASSCAL “Texan” single-channel recorders mated to a vertical 4.5-Hz geophone Supported by USGS, NEHRP ERP and IRIS-PASSCAL

30 J. Louie UNR Geol492/692 Spring 2005 Los Angeles Transect: Levee Effects  V 30 levee: 245 m/s  V 30 non-levee: 241 m/s

31 J. Louie UNR Geol492/692 Spring 2005 Los Angeles Transect: Results

32 J. Louie UNR Geol492/692 Spring 2005 V 30 vs Geologic Unit  Large V 30 variation inside each unit  Large V 30 variation between units

33 J. Louie UNR Geol492/692 Spring 2005 V 30 vs Soil Type  In general, large V 30 variation within units  Units 2 and 5 may be NEHRP D  Large V 30 variation between units

34 J. Louie UNR Geol492/692 Spring 2005 Las Vegas route from Cheyenne to Tropicana 1-km-deep basin 3-km-deep basin Supported by DOE-LLNL and IRIS- PASSCAL Shallow Shear-Velocity Transects

35 J. Louie UNR Geol492/692 Spring 2005 49 velocity profiles to correlate with stratigraphy Las Vegas Transect Measurements

36 J. Louie UNR Geol492/692 Spring 2005 Transect Data High-velocity picks at >0.4 sec period are unreliable. Picks at 0.1-0.3 sec illustrate velocity differences to 100 m depth.

37 J. Louie UNR Geol492/692 Spring 2005 Some correlation to faulting, soil type? Las Vegas Transect

38 J. Louie UNR Geol492/692 Spring 2005 Geologic Info to Predict V s NSL, July ‘03, sponsored by LLNL  Can soil maps predict V s ?

39 J. Louie UNR Geol492/692 Spring 2005 Does extrapolating V s work?  V s assigned to soil-map units using central-City measurements.  Later, outlying measurements (B. Luke, UNLV) not predicted by maps.

40 J. Louie UNR Geol492/692 Spring 2005 Does extrapolating V s work?  V s assigned to soil-map units using central-City measurements.  Later, outlying measurements (B. Luke, UNLV) not predicted by maps. 1 2 3 4

41 J. Louie UNR Geol492/692 Spring 2005 Most of Strip, Downtown; south side of Valley only 79 sites total 1000 well logs & geologic mapping Las Vegas Transect

42 J. Louie UNR Geol492/692 Spring 2005 How to Extrapolate Shallow V s  Correlate 75 Vs measurements against stratigraphic model.  Stratigraphy interpolated between >500 water-well logs.

43 J. Louie UNR Geol492/692 Spring 2005 Extrapolated vs. Measured  Comparisons along Cheyenne-to-Tropicana transect.

44 J. Louie UNR Geol492/692 Spring 2005 No correlation between V 30 and geologic map. Las Vegas Transect

45 J. Louie UNR Geol492/692 Spring 2005 Correlation with clay soils, caliche in Las Vegas? Las Vegas Transect

46 J. Louie UNR Geol492/692 Spring 2005Summary  ReMi allows rapid seismic shaking-hazard classification, as required by IBC2000.  Long ReMi transects can geophysically characterize spatial variations in shaking hazard.  Mapped soil and geologic units do not reliably predict the measured V 30.  Our measurements suggest one can use river gradients, Quaternary thickness, or alluvial fan composition to predict shallow velocities.

47 J. Louie UNR Geol492/692 Spring 2005 Example of public outreach: Discoveries and Breakthroughs Inside Science, news shorts funded by AIP, AGU, etc.Outreach KFSN-TV Fresno, CA KGBT-TV Harlingen, TX KJTV-TV Lubbock, TX KTRK-TV Houston, TX KNBC-TV Burbank, CA KNSD-TV San Diego, CA KQTV-TV St. Joseph, MO KNTV-TV San Francisco, CA KRQE-TV Albuquerque, NM KTSM-TV El Paso, TX KTVN-TV Reno, NV KWQC-TV Davenport, IA KXAS-TV Fort Worth, TX WAGM-TV Presque Isle, ME WTEN-TV Albany, NY WCAU-TV Philadelphia, PA WCMH-TV Columbus, OH WCYB-TV Bristol, VA WEWS-TV Cleveland, OH WFTS-TV Tampa, FL WLUK-TV Green Bay, WI WBBH-TV Fort Myers, FL WHIO-TV Dayton, OH WIS-TV Columbia, SC WJAR-TV Cranston, RI WLBT-TV Jackson, MS WMAQ-TV Chicago,IL WNBC-TV New York, NY WNCN-TV Raleigh, NC KTSM-TV Omaha, NE WPBN-TV Traverse City, MI WSYM-TV Lansing, MI WTVJ-TV Miami, FL WVIT-TV Hartford, CT WVTM-TV Birmingham, AL WXYZ-TV Southfield, MI WJXT-TV Jacksonville, FL WTXL-TV Tallahassee, FL WIVT-TV Binghamton, NY WEVV-TV Evansville, IN WCJB-TV Gainesville, FL WPXI-TV Pittsburgh, PA CHAT-TV Medicine Hat, ALB K. Heineman, NewsProNet, Producers Technology Transfer: Commercial ReMi is now in use by geotechnical consultants and agencies worldwide.

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