CyberShake BBP Verification

This page documents our CyberShake Broadband Platform validation work, running the BBP validation events through CyberShake.

Events

We plan to run the following events from the BBP:

• Northridge
• Landers
• North Palm Springs
• Whitter
• Chino Hills

Verification and Validation

Planned process will involve verification and validation stages.

• Verification: Compare CyberShake broadband seismograms to Broadband Platform seismograms
• Validation: Compare CyberShake broadband seismograms to observed seismograms

Validation Process

For each of the 5 BBP validation events listed above, go through the following process:

• Run the BBP validation event with the Graves & Pitarka modules to produce BBP results for comparison.
• Review the BBP validation data for the event, including station list and seismogram files and validation results from GP method for this event.
• Identify about 10 stations from the BBP station list that have observed seismograms to run in CyberShake.
• Modify station list low-pass filter to 50 Hz.
• Use the Vs30 values from the BBP station list for both the low-frequency and high-frequency site response in CyberShake, for consistency.
• We will use CVM-S4.26.M01 as the velocity model for CyberShake.
• Run one realization using the SRF file which is generated by the BBP when run with one realization.
• Create an ERF in the CyberShake database containing all the validation events, with a unique source and rupture ID for each one.
• Save the SGTs in case we want to run additional realizations later.
• To interface with the BBP tools for generating data products, convert the CyberShake seismograms into BBP format seismograms

Data Products

The CyberShake method calculates two component seismograms. Broadband platform supports three component seismograms. We will convert CyberShake 2 components to 3 components by duplicating the N/S component in the vertical component data.

We will produce the following data products to compare CyberShake results with BBP results:

• ts_process plot, comparing traces and response spectra.
• RotD50 comparison plots
• Goodness-of-fit bias plots
• Map of GoF, by station

Northridge

A KML of the Northridge stations is available here. Selected stations are in orange. The BBP station list file for these stations is available here.

We made the following modifications to the default BBP platform to support better comparison to the BB CS results:

• Changed the BBP LF and HF seismogram length to 500 sec / 50,000 timesteps
• Modified the filtering so the merge frequency is 1.0 Hz and phase=0

3D comparisons

Below are comparisons using the CVM-S4.26.M01 model in CyberShake.

Stage	Seismogram comparison
Filtered high-frequency acceleration with site response
Low-frequency velocity
Broadband velocity

BBP LA Basin 1D comparisons

Below are comparisons using the BBP 1D LA Basin model in CyberShake with no interpolation. We also:

• Modified the CyberShake filtering scheme to match the BBP filtering scheme, which uses a high-pass filter for the HF at around 0.89 Hz and a low-pass filter for the LF at about 1.11 Hz.
• Modified the CyberShake low-frequency site response to use the high-frequency PGA values, consistent with the BBP approach.

We ran SCE with both the original 1D model, and a modified version (File:Modified nr02-vs500.txt)

Stage	BBP vs CS, original 1D	BBP vs CS, modified 1D
Low-frequency (velocity)
Low-frequency with site response (velocity)
Low-frequency with site response and filtering (velocity)
High-frequency with site response and filtering (velocity)
Broadband results (velocity)

Comparable dt

We reran our comparisons with the same dt (0.1) for SCE in CyberShake and the BBP:

Stage	BBP vs CS, original 1D
Low-frequency with site response and filtering (velocity)
High-frequency with site response and filtering (velocity)
Broadband results (velocity)

Other sites

	RO3 (5/170 interchange)	PEL (Santa Monica/Highland)
Low-frequency (velocity)
Low-frequency with site response (velocity)
Low-frequency with site response and filtering (velocity)
High-frequency with site response and filtering (velocity)
Broadband results (velocity)

Halfspace comparisons

Seismograms

Point source. Red = AWP, Black = RWG.

Unfiltered
Filtered

Northridge BBP validation event. Red = AWP, Black = RWG.

Unfiltered
Filtered

SGTs

	X-component	Y-component
Adjusted mu in AWP
Unadjusted mu in AWP		File:SCE hspace sgts rwg v awp uncorrmu y.png

Uncorrected mu

Modified 1D velocity model

RWG and AWP SGTs, using SGT headers with uncorrected mu values

Filtered seismograms (red = AWP, black = RWG)

Point source
Northridge

SGTs (red = AWP, black = RWG)

X	Y

1Hz source plots

To reduce ringing effects, we started using an impulse low-pass filtered at 1 Hz.

All the plots below are of SGTs.

Slow halfspace

The plots below were calculated using a halfspace model with Vp=1500, Vs=750, rho=2200.

Qs=37.5, Qp=75.0

X	Y

Qs=10000, Qp=20000

X	Y

4-layered model

Next we ran with a 4-layered model:

Thickness(km)   Vp      Vs      rho     
0.2500          2.4000  1.0000  2.2500  
0.7000          3.7000  1.8000  2.4500  
1.5000          4.7500  2.4000  2.6000 
2.5000          5.4000  3.0000  2.6500 
999.00          6.2000  3.5000  2.7200 

Qs=10000, Qp=20000

X	Y

Qs=0.05Vs, Qp=2Qs

X	Y

Qs=0.05Vs, Qp=2Qs

Unadjusted mu and lambda used for stress->strain conversion. This was accomplished by removing adjustment factors in the SGT kernel.

Depth	X	Y
Shallow (5 km)
Deep (15 km)

12-layered model

   Vp      Vs      rho         Depth to layer bottom (km)
  2.4000   1.0000   2.2500     0.250001
  3.1000   1.4000   2.3000     0.450001
  3.3495   1.5560   2.3750     0.550001
  3.7000   1.8000   2.4500     0.950001
  3.9190   1.9285   2.5125     1.050001
  4.2000   2.1000   2.5750     1.450001
  4.4483   2.2343   2.5875     1.550001
  4.7500   2.4000   2.6000     2.450001
  4.9150   2.5565   2.6100     2.550001
  5.1000   2.7500   2.6200     3.450001
  5.2426   2.8661   2.6350     3.550001
  5.4000   3.0000   2.6500     4.950001
  6.2000   3.5000   2.7200     9999.999999

Qs=0.05Vs, Qp=2Qs

Unadjusted mu and lambda used for stress->strain conversion.

Depth	X	Y
Shallow (5 km)
Deep (15 km)

14-layered model

   Vp      Vs      rho      Depth to layer bottom (km)
  1.6447   0.5378   2.0600     0.050001
  1.8893   0.7115   2.1500     0.150001
  2.3653   0.9766   2.2500     0.250001
  3.1000   1.4000   2.3000     0.450001
  3.3495   1.5560   2.3750     0.550001
  3.7000   1.8000   2.4500     0.950001
  3.9190   1.9285   2.5125     1.050001
  4.2000   2.1000   2.5750     1.450001
  4.4483   2.2343   2.5875     1.550001
  4.7500   2.4000   2.6000     2.450001
  4.9150   2.5565   2.6100     2.550001
  5.1000   2.7500   2.6200     3.450001
  5.2426   2.8661   2.6350     3.550001
  5.4000   3.0000   2.6500     4.950001
  6.2000   3.5000   2.7200  9999.999999

Depth	X	Y
Shallow (5 km)
Deep (15 km)

Related Entries

• CyberShake
• Broadband Platform