Developing ENA GMPE s Using Broadband Synthe=c Seismograms from Finite- Fault Simula=ons

Transcription

1 Developing ENA GMPE s Using Broadband Synthe=c Seismograms from Finite- Fault Simula=ons Art Frankel U.S. Geological Survey SeaFle, WA NGA- East workshop Oct 29, 2014 From Frankel (2009) 1

2 ENA broadband synthe=cs, M4.5, M5.5, M6.5, M7.5 Stochas=c extended source synthe=cs at high frequency Determinis=c extended source synthe=cs from reflec=vity for 1D model at low frequency Cross over frequency varies with magnitude: 0.8 Hz for M7.5, 2.4 Hz for M6.5, 3 Hz for M5.5 and M4.5 (same as used in WUS) Similar procedure as used in Frankel (2009) and compared to NGA West 1 (M ). Compared with SA s and FAS of Northridge, Loma Prieta, and Izmit earthquakes in Hartzell et al. (2011). I also compared SA s from ENA synthe=cs with Riviere du Loup and Saguenay SA s. Stochas=c finite- fault por=on 200 bar stress drop for all magnitudes M Geometrical spreading as in FEA96: R - 1 for 0-70 km, flat km, R > 130 km (from Atkinson and Boore, 1995) Q= 680f 0.36 (from Atkinson and Boore, 1995) Data from Charlevoix earthquakes support R - 1 out to 80 km (Frankel, paper submifed to BSSA) Scaled fault area from WUS area based on twice sta=c stress drop 270 x 270 m sub- event size, result not sensi=ve to this Used fractal distribu=on of stress drop Hard- rock site condi=on, Vs30= 2800 m/s, kappa=

3 Determinis=c finite- fault por=on Used SE Canada crustal model from Hartzell et al. (1994) Used Zhu frequency- wavenumber integra=on code 270 m x 270 m sub- event size Fractal slip on fault; secant rupture velocity varia=ons propor=onal to slip varia=ons Dynamic stress drop constant with moment. Used average slip velocity of 5.4 m/s. Slip velocity/rupture velocity propor=onal to dynamic stress drop. Slip velocity of 2.7 m/s fits NGA West 1 data (M ) and gives similar rise =mes as Somerville et al. (1999). Runs for ver=cal strike slip and for 45 degree thrust faul=ng. M Slip (m) 6 Depth (km) 30 0 Distance along strike (km) 80 0 Rupture initiation time (s) 3

4 Table 2. Velocity Model (from Hartzell et al., 1994) Vp (km/s) Vs (km/s) Density Thickness Q p Q s (g/cm 3 ) (km) Example of combining determinis=c and stochas=c synthe=cs to make broadband (0-20 Hz) synthe=c accelera=on waveforms From flat-layered velocity model Based on geometrical spreading and Q model combined with matched filter At 0.8 Hz From Frankel (2009) Example for M7.5 crustal earthquake 4

5 Distance metric is closest distance to rupture, Rrup Receivers distributed in azimuth and distance Used geometrical average of SA from two horizontal components Fault dimensions and depth ranges of ruptures M4.5: source size 1.23 x 1.23 km; 5-6 km depth SS and thrust; km depth SS; hypocenter at base of rupture zone M5.5: source size 3.9 x 3.9 km; 4-8 km depth; 6-10 km depth; SS and thrust; 9-13 km depth SS; hypos at mid point and base of rupture M6.5: source size 14.3 x 9.5 km; 5-15 km depth; hypos at base and middle; SS and thrust M7.5: thin aspect ra=o 119 by 12 km; depth 5-17km; SS and thrust; hypo near base of rupture M7.5: thick aspect ra=o: 80 by 25 km; depth 5-30 km; SS and thrust; hypo near base of rupture 5

6 5 Hz SA from synthetics; M4.5 black; M5.5 green; M6.5 red; M7.5 blue Solid lines: Frankel et al. (1996); dashed and dashed dot lines are Atkinson and Boore (2006) 140 and 200 bars, respectively 1 Spectral Acceleration (g) e Closest Distance to Rupture (km) 1 Hz SA from synthetics; M4.5 black; M5.5 green; M6.5 red; M7.5 blue Solid lines: Frankel et al. (1996); dashed and dashed dot lines are Atkinson and Boore (2006) 140 and 200 bars, respectively Spectral Acceleration (g) e Closest Distance to Rupture (km) 6

7 M4.5 1 Hz SA Red triangles are data M Vs30 >= 760 m/s; from NGA East database Spectral Acceleration (g) e-05 1e Closest Distance to Rupture (km) M5.5 1 Hz SA 1 Red triangles are data M Vs30 >= 760 m/s; from NGA East database 0.1 Spectral Acceleration (g) e Closest Distance to Rupture (km) Sparks Oklahoma earthquake not included 7

8 M4.5 5 Hz SA 1 Red triangles are data M Vs30 >= 760 m/s; from NGA East database 0.1 Spectral Acceleration (g) e-05 1e Closest Distance to Rupture (km) M5.5 5 Hz SA 1 Spectral Acceleration (g) e-05 Red triangles are data M Vs30 >= 760 m/s; from NGA East database Closest Distance to Rupture (km) 8

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10 11/5/14 10

11 distance decay of long- period SA sensi=ve to source depth 11

12 4-8 km rupture depth 9-13 km rupture depth GMPE s will be specified by median SA values in distance bins, at each period, for the four magnitudes simulated (4.5, 5.5, 6.5, 7.5) 12

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14 Analysis of coda normalized S- wave amplitudes from Charlevoix earthquakes (waveforms and event parameters from Geological Survey of Canada) 14

15 The best-fit line is R ± Observations of coda-normalized S-wave amplitudes from Charlevoix earthquakes From Frankel (paper submitted to BSSA) The best-fit line is R-1.35 ± 0.14 Observations of coda-normalized S-wave amplitudes from Charlevoix earthquakes From Frankel (paper submitted to BSSA) 15

16 The best-fit line is R-1.05 ± 0.15 Observations of coda-normalized S-wave amplitudes from Charlevoix earthquakes From Frankel (paper submitted to BSSA) 1 Hz Fourier spectral amplitudes from the observed waveforms (black dots) and synthetics (open symbols) for the Rivière du Loup earthquake. The reference line corresponds to R

17 1 Hz Fourier spectral amplitudes for 6/13/2003 earthquake, from observed waveforms and synthetics A physically- plausible model Uses flat- layered synthe=cs from finite faul=ng with realis=c slip distribu=ons and rupture histories: captures direc=vity effects (e.g., forward direc=vity pulses), radia=on pafern effects, varia=ons with slip distribu=on and hypocenter, crustal and Moho reflec=ons, and surface waves Uses constant stress drop scaling with moment: constant slip velocity with moment for determinis=c part; constant Brune stress drop (200 bars) for sub- events in stochas=c part Stochas=c por=on has finite- faul=ng scaling consistent with omega - 2, constant stress drop scaling (high- frequency spectral energy at any frequency propor=onal to fault area) Produces satura=on with magnitude at close- in distances due to finite faul=ng; satura=on less prominent at lower frequencies Uses R - 1 spreading out to 70 km for stochas=c por=on, consistent with Charlevoix observa=ons 17

18 Predicted response spectra at site A near Waste Treatment Plant; Rupture is located below the site 18

19 11/5/14 Predicted response spectra for site A near Waste Treatment Plant Rupture is near edge of basin For NGA West : Vs30= 450 m/s; default Z2.5 and Z1.0; used S. Harmsen s code One of the slip distribution and rupture initiation models used in the M6.8 Rattlesnake Hills West simulations. Variations in secant rupture velocity proportional to slip variations Did 10 simulations for each Fault random draw from 5 slip distributions and random hypocenters in bottom half of fault plane 19

20 Constant Stress-Drop Model for Producing Broadband Synthetic Seismograms 671 (a) acceleration velocity cm/sec/sec cm/sec (b) cm/sec/sec cm/sec (c) cm/sec/sec cm/sec time after origin time (sec) time after origin time (sec) Figure 7. Acceleration and velocity synthetics for three sites at 3 km R jb from fault for the M 7.5 simulation where the hypocenter is located 38 km from the southern end of a 150 km long fault. The top trace in each panel is the east west component (perpendicular to fault strike, i.e., fault normal). The bottom trace in each panel is the north south component (parallel to fault strike). (a) The station located 3 km from the north end of the fault. (b)the station located 3 km from the middle of the fault. (c) The station located 3 km from the south end of the fault.seismograms are displaced vertically on each plot for clarity.note strong pulses on the fault-normal component for all the stations. This pulse is especially dominant on the fault-normal velocity synthetics for these receivers. tical strike-slip, surface-rupturing faults used here for M 7.5 and M 6.5, the closest distance to the fault is equal to the Joyner Boore distance R jb (Joyner and Boore, 1981). The hypocenter where the rupture starts is closer to the southern end of the fault. On the acceleration traces, the long-period forward directivity pulse is most apparent in the station off of the north end of the fault. The peak acceleration for the station to the south is significantly smaller. It is clear how rupture directivity causes large variations in ground motions for stations at different azimuths but identical distances from the closest portion of the fault. The accelerogram for the station near the middle of the fault has a more extended duration than those off the ends of the faults, again an expression of the differences caused by rupture directivity. The velocity traces demonstrate the large pulses on the fault-normal component for these three receivers. The peak velocity is largest on the station to the north, even though it is farther from the hypocenter than the other stations. This is caused by the larger portion of the fault between the hypocenter and the northern station. For stations at other azimuths (not shown in Fig. 7), the fault parallel peak velocities are closer to the fault-normal ones. Figure 8 displays synthetic accelerograms at three different distances from an M 7.5 earthquake. The decrease 20