UCVM Vs30

We are reviewing the algorithms used to calculate Vs30 in UCVM.

UCVM CS173 Model-based Vs30

Vs30 based on tiled models queried at 1m spacing 0-29m depth using slowness calculation

UCVM Etree Vs30 Map

Vs30 from UCVM etree map, based on Willis 2006 map and Wald Topography (outside California)

Introduction

There may be an issue with how UCVM calculates Vs30 values. Presently UCVM uses the following formula:

1. sum(Vs sampled from [0,30] at 1 meters, for 31 total values) / 31

Rob has suggested that the correct formula should be:

1. 30 / sum(1 / (Vs sampled from [0, 30) at 1 meters, for 30 total values))

This can have a significant impact for Vs30 calculations. For the BBP1D model, UCVM calculates the Vs30 as 932m/s, whereas Rob's formula calculates it as 862m/s.

Another approach was used in CyberShake Study 15.12, in conversations with Rob:

1. Vs30 = 30 / Sum (1/(Vs sampled from [0.5,29.5] in 1 meter increments, for 30 total values)).

Points for comparison

We have selected 6 points to compare Vs30 as generated using the CyberShake approach (using half-meters) to other UCVM approaches.

• Input points for ucvm_query:

34.1484 -118.1712 34.5570 -118.1250 34.0192 -118.2860 34.6402 -118.9192 36.1397 -120.3602 34.2667 -119.2285

lat	lon	Velocity model	CyberShake-generated Vs30	UCVM 18.5 Vs30 from Model	UCVM Vs30 etree.map (Wills 2006)	UCVM Vs30 etree.map (Wills 2015)
34.148426	-118.17119	CVM-S4.26.M01	838.8	821.328	748.00	710.1 (cvmsi)
34.557	-118.125	CVM-S4.26.M01	2573.6	2573.634	497.68	402.1 (cca)
34.0192	-118.286	CVM-S4.26.M01	313.1	310.574	280.0	293.5 (cvmsi)
34.64021	-118.91919	CCA-06	3393.9	3331.251	748.0	710.1 (cca)
36.13968	-120.36015	CCA-06	2277.2	2279.326	349.0	293.5 (cca)
34.26667	-119.22848	CCA-06	902.3	902.013	280.0	325.5 (cca)

Querying cs173 slow due to the fine resolution

To run on max memory on hpc cluster nodes

#!/bin/bash
#SBATCH -p scec
#SBATCH --ntasks=1 #number of tasks with one per processor
#SBATCH -N 1 # number of nodes
#SBATCH --mem 0 # Set to unlimited memory
#SBATCH --time=12:00:00
#SBATCH -o ucvm2mesh_mpi_%A.out
#SBATCH -e ucvm2mesh_mpi_%A.err
#SBATCH --export=NONE
#SBATCH --mail-user=maechlin@usc.edu
#SBATCH --mail-type=END

cd /auto/scec-00/maechlin/ucvmc185/utilities
srun -v --mpi=pmi2 /auto/scec-00/maechlin/ucvmc185/utilities/plot_vs30_map.py -b 30.5,-126.0 -u 42.5,-112.5 -s 0.01 -a s -c cs173 -o vs30_cs173.png
-bash-4.2$ 

Related Links:

Plot command used to plot_vs30_map. ./plot_vs30_map.py -b 30.5,-126.0 -u 42.5,-112.5 -s 0.05 -a s -c cs173 -o vs30_cs173.png

Scott posted vs30 values from CyberShake here: http://scec.usc.edu/scecpedia/CyberShake_Study_15.12#Vs_values_v2.0

Related Entries

• UCVM