Array Response Functions
with ArrayGUI
Nawa Dahal
Robert Martin-Short
Sharmin Shamsalsadati
Voon Hui Lai
IRIS Short Course
Aug, 2015
Array Seismology
Numerous seismometers placed at discrete points in a
well-defined configuration to record ground motions.
Applications:
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Lower the detection threshold of global earthquakes
Detect and identify nuclear explosion
Detect phases that usually are not detected by single station
High-resolution tomographic images on regional scale
Detect small-scale structures in the Earth’s mantle
Use in ambient noise interferometry studies
New trend in
seismology
Challenges in Array Seismology
• Need a good array configuration to ensure
wave coherency.
• Need an easy way to check station quality for
large number of stations.
• Need to determine the direction of seismic
sources (particularly for ambient noise
interferometry)
Importance of choosing
array configuration
to study scattered tsunami
waves
All stations
All stations
Dataset: ALBACORE OBS Array
9 selective stations
Higher frequency
Introducing ArrayGUI
One stop to access array and station
quality
PSD plots
Input:
ARFs
Specify
1. Network /
Area of interest
2. Time
interval
Interactive
python GUI
Beamforming analysis over
time
(future development)
Screen shots from the example GUI:
Polygon drawing tool:
select array geometry
Look at station metadata; create PSD
plots
Create response function for stations of
interest
Note: Assure user already has the data, in future, call use GUI to
download this too
User inputs network code, time
window
GUI displays
network map
User choose array
geometry
Good
ARF
User makes
ARF
User creates
beamforming plot
Option to view
station
PFD/PDF
plots, and
metadata
Draw a
Bad ARF
Set array response function defaults: frequency range of
interest, approximate phase velocity.
Also set PSD and station metadata defaults.
.
A Python GUI
• Tkinter module (Tk GUI toolkit)
• Contains functionality (ex: make buttons, menus, pop-up windows)
• Easy to use within code organized in classes: each method can
describe a different GUI aspect.
Buttons link to commands:
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Make new maps on the fly
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Allow selection of individual
stations
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Link to Obspy modules and to
IRIS PDF/PSD noise toolkit
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Download/analyse waveforms
from the selected stations
Existing
Problem with Existing
Toolstools
• Open source codes but not integrated. (ref)
• Established codes can be optimized
• Improve workflow
IRIS Tools:
• IRIS DMC PSD plot
• Plot ARFs using obspy function.
• Example of beamforming in backprojection tools. No physical
product except personal Matlab scripts.
Power Spectral Density plot
• Allows analysis of noise
characteristics of a
selected station over a
selected time window
• User select station in
‘station options’ window;
inputs time range.
• Program links to IRIS
noise toolkit; produces
enhanced PSD plot
• Array response function
Array Response Function (ARF)
• Purpose: Access quality of array configuration
(geometry, interstation distance, wave frequencies)
• Input: station coordinates, frequencies, limits of wavenumber
• Main code: (obspy-array_transff_wavenumber)
• Output: plot of ARF, list of parameters, and map
Station list.
Frequency.
Parameters.
Future development: Beamforming
Analysis
Purpose: Determine signal source directivity
over time
Steps:
-Fix slowness, frequencies, stations
-Perform beamforming using
“delay-and-sum” method across
all back-azimuths
-Plot relative power for each
back-azimuth over time
Rewrite existing MATLAB scripts into
Python (consider using HPC)
Potential Applications/Users
• Simplify usage of large array data sets
• Detect direction of ambient noise sources
• Facilitate education and outreach
Thank You!