Southern California Seismic Velocity Model Vertical Profiles

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Southern California Velocity Models Evaluation Studies


Evaluation of the southern California seismic velocity models through simulation of recorded events

Y Lu, Y Ben-Zion, Validation of seismic velocity models in southern California with full-waveform simulations, Geophysical Journal International, Volume 229, Issue 2, May 2022, Pages 1232–1254,

Recently Developed Southern California Velocity Model (Fang et al.)

The Fang et al paper defines a Southern California Plate Boundary Velocity model. The max depth is 20 km; the model should be merged with a regional model to have information below that depth but this will require smoothing between models. We are looking at the Vp, Vs models of the Fang et al. (2016) pape. , and also the Fang et al. (GJI, 216, 609–620, doi: 10.1093/gji/ggy458.2019) paper that has better Vs results, and classify the results using K-means clusters as done by Eymold and Jordan (2019).

Ely/Jordan Geotechnical Layer method

Ely/Jordan developed a method for restoring lower Vs values from velocity models. The near surface Vs values are defined from the Vs30 for the site, and then smoothly tapered with the underlying, deeper, velocity models. This was developed to restore low Vs values removed to make the tomography calculations more efficient.

Modifying the Geotechnical Layer

Kim Olsen's group has publish papers on how to modify the CVM-S4.26.M01 near surface properties to get a better fit to recorded ground motion records. His group recently published two companion papers in GJI:

One the study finds that a 700-1,000 m tapered GTL produces better results than a 350 m GTL for La Habra. The other paper is derived from his High-f efforts, a 0-5 Hz study on La Habra, where we quantify the effects on ground motions from topography, Q(f), and GTL using a source that Rob generated long time ago. Here, he advocates for a Qs=(0.075,1.0)Vs model. The papers were part of Kim's student Zhifeng Hu's PhD thesis.

The page below contains plots of vertical profiles for some southern California Sites, with their current Vs values from CVM-S4.26.M01, and with the Ely/Jordan modifications at taper depth 350m (which is the default), and taper depth of 700m (which Kim recommends) are plotted here.

Vs and Q relations

Among Kim Olsen's test models, the Qs=0.075 Vs model was optimal for frequencies lower than 1 Hz,

Qs=0.05 Vs seems to over-dampen a bit.

Options for Generating Vertical Profiles

  1. UCVM Website

This site can plot vertical profiles, and the images and data files can be downloaded. But it is interactive.

  1. UCVM plot vertical profile

UCVM (and UCVM docker images) have a plotting script that inputs a lat,lon, depth range, spacing, and model name, and outputs images, and data files. This is probably the simpliest way to retrieve a group of several hundred sites.

  1. UCVM ucvm_query

UCVM basic query is ucvm_query. Users creates and input file, that lists every query point (lat,lon,depth) and then call ucvm_query with the list of query points. This is the most basic way to query the CVMs for information.

Both the UCVM website and ucvm plotting create png plots, and metadata files with the data being plotted. The metadata files can be difficult to interpret. SCEC has a Python3 script that combines posted on GitHub at:

UCVM Website (prototype)

All the currently available velocity models are registered into this webviewer. Select a velocity model of interest using the dropdown menu.

A menu selection asks if you want to query the model by elevation or by depth. Default for CVM-S4, CVM-S4.26, and CVM-S4.26.M01 are positive numbers below earth surface. If you query by elevation steps are positive above Mean Sea Level, and negative downward.

Accessing Docker Images

Docker is a software system that enables users to run Linux software on Mac, Windows, and Linux systems. Science applications are distributed as "Docker Images" which include all the required software including the Operating system, compilers, and science software. Docker Images can be run using a free software called a Docker Client. Docker Client software is available for Mac, Windows, and Linux systems, and be downloaded for free from Docker:

Docker has largely replace "Virtual Box" technology which was used in the past to run Linux software on Mac and other systems.

Directions for running UCVM Docker images are posted:

Docker Client software:

SCEC Community Fault Model w/ Hauksson Catalog

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