HighF v14.12

This page collects information about a proposed high frequency verification and validation exercise. Planning started in Dec 2014.

Goal

Most regional scale deterministic earthquake simulation verification and validation exercises have been done at frequencies 1Hz or lower [1] [2]. With the introduction of high performance CPU and CPU-GPU wave propagation codes, there has been significant recent progress running simulations up to 4Hz. As we increase the capabilities of our deterministic earthquake simulation codes, we need to re-evaluate the codes performance at these higher frequencies that are now possible. The goal of this activity is to evaluate the performance of multiple wave propagation codes that are capable of simulation regional scale earthquakes at frequencies 4Hz+.

Approach

High frequency simulations introduce several code modifications intended to more accurately model the physics of high frequency earthquake wave propagation simulations. Modification to existing wave propagation codes to support 1Hz+ simulations include:

• Source descriptions with energy above 1Hz
• Small scale heterogeneities in the 3D velocity models
• Frequency dependent attenuation
• Near fault plastic yielding
• Large displacement plastic yielding

To help isolate the impact of each of these changes, we propose to start with simple (possibly unrealistic) high frequency (4Hz) ground motion simulations and compare the simulation results produced by different methods. Then we will introduce these modifications one at a time, as a way if isolating the impact of each change individually.

Problem Statement

We have defined common input parameters for use by both AWP-ODC, and Hercules. The problem statements includes the following parameters:

1. Simulation Region
2. Source Description
3. Station List
4. Velocity Model
5. Simulation Duration
6. Simulated Frequency Range
7. Sample per Wavelength

Simulation Region

The simulation region four corners are:

• -119.288842 34.120549
• -118.354016 35.061096
• -116.846030 34.025873
• -117.780976 33.096503

Volume size:

• 180,000 m x 135,000 m x 61,875 m = 1.503e15 m3

Source Description

We will use a rough-fault dynamic-rupture-based point source produced by Zheqiang Shi (SDSU) that has frequencies above 4Hz, scaled to Mw5.1 La Habra. The source is plotted and defined in the following files. These show the source trimmed, low-pass filtered (fc=5Hz, Butterworth, 2 forward passes, 4 poles), 4300 points, dt=0.001s (and plot of what is should look like).

• Time domain Plot of Selected Source
• Source Frequency Domain Plot w/ and w/o Filtering
• Data File For 5Hz Plot (Source after filtering)

1D Velocity Model Definition

The first velocity model will be modeled on a 1D model of the Los Angeles Basin used in on the Broadband Platform project. The model was smoothed to eliminate sharp contrasts between layers.

• Diagram of smoothed 1D Model (pdf)
• Diagram of smoothed 1D Model showing Layers (pdf)
• 1D model data file (20m resolution) (rtf)

Definition of Los Angeles Basin 1D velocity models used in the Broadband Platform project:

• Broadband_File_Format_Guide#Velocity_Model_File

Station List

We developed a list of ground motion observations for the La Habra earthquake. A description of the methods used to create this merged site list are provided at Selection of La Habra Ground Motion Observations.

This site list is based on use of publicly posted data sets for the La Habra event. There should be on-scale accelerometer ground motion data at all of these sites for the La Habra mainshock. We have not yet plotted all data to visually confirm the data is above noise, and on-scale. This list combine all channels available from SMO and SCECDC for the La Habra Event using only acceleration instruments within the simulation region:

• Total SMO and SCECDC [HN] Stations in simulation region : 356
  • Merged (SMO + SCECDC) Site KML Map (KML File)
  • Merged (SMO + SCECDC) Site List (TXT File)

In these merged data sets, we will manage the observational data separately until we have confirmed the processes of each data set. The SMO data will be in the processed V2 cosmos format. The SCEDC data will be in Counts that will need to be converted to acceleration using a gain factor in the metadata file.

We will compare our signal processing between data sets for some of the overlapping data sites where we have both SMO data and SCEDC data.

Simulation Box / Velocity Model

Parameter	Value	Notes
Dimensions (km)	180 x 135 x 61.875 (31 km for 1d Model)
Bounding Box (LL)	-119.288842 34.120549, -118.354016 35.061096, -116.846030 34.025873, -117.780976 33.096503
Rotation Angle	39.9
UCVM Version	14.3.0	No heterogeneities
Velocity Model Versions	CVM-S4v26
Miniumum Vs	500 m/s
Samples per wavelength	6 to 7 - AWP	10 to 12 - Hercules

Point Source Parameters

Parameter	Value	Notes
Event Name	La Habra
Mw	5.1	Ref: http://www.scsn.org/2014lahabra.html
Moment	5.764 E+23 Dyne-cm	Source: En-Jui
Origin Time	2014/03/29 04:09:42.97	Source: En-Jui
Origin Location	-117.930; 33.922; 5.0km	Source: En-Jui
Strike/Dip/Rake	239/70/38	Source: En-Jui, based on review of aftershock sequence
Rise Time	0.75 s

Solver Parameters

Parameter	Value	Notes
Frequency	4.0 Hz
Simulation Length (Duration)	100 s
Delta T	0.005
Plane Output Resolution	250m
I/O Print Rate	every 10 steps
Station List	TBD
Software Version	TBD

Fig 1:Location of La Habra Main Shock and aftershocks, used to select preferred fault plane solution. (Image Credit: En-Jui Lee)

High-F VandV Exercise Planning Documents (2015)

• High-F V and V Exercise Description - Jan 2015 (pptx)

High-F Project Plan (2012)

• Original High-F Project Plan (pdf)
• Original High-F Project Plan (docx)

Agreements Needed

• Simulation Volumes
• Rotation Angle
• Projections used
• Points per wavelength used
• Number and location of sites used for ground motion comparison
• Proposed Station List to save results
• La Habra Point Source parameters
• Currently available code capabilities in GPU codes
  • small scale heterogeneities
  • FDQ
  • Plasticity
  • dynamic rupture source
• V and V exercise stages - need to be reviiewed and approved

Related Entries

• High-F Project
• CME Project
• AWP-ODC
• Hercules

References Used

• Taborda, R. and J. Bielak (2013). Ground-motion simulation and validation of the 2008 Chino Hills, California, earthquake, Bull. Seismol. Soc. Am. 103, no. 1, 131–156, doi 10.1785/0120110325.