West Coast/Alaska Tsunami Warning
Center
Operations Manual
NOAA/NWS/WCATWC
910 South Felton Street
Palmer, Alaska 99645
http://wcatwc.arh.noaa.gov
Section
4.1.13 – pick_wcatwc
Date Written: 12/2000
Development Language: MicroSoft C/C++ v7.0
Necessary Rings:
Input Ring - WAVE_RING;
reads TYPE_TRACEBUF format messages
Output
Ring - PICK_RING; writes TYPE_PICKTWC and TYPE_PICK_GLOBAL format messages
Output Ring - ALARM_RING;
writes TYPE_ALARM format messages
Necessary Data Files:
StaFile - picker
configuration file
StaDataFile - seismometer
location, elevation, etc.
AlarmFile – multi-station alarm parameters
Initialization File:
pick_wcatwc.d
- read on module start-up
Module Description:
This earthworm module is the latest re-write of the P-picker
used at the West Coast/Alaska Tsunami Warning Center since the early 1980's. The
P-picker was developed by Veith at Teledyne GeoTech. Several additions have
been made regarding magnitude determinations, automatic calibrations, and
alarming, but the P-pick algorithm itself is basically the same as first
proposed.
Short period filtering is provided by this module for broadband data when
specified in the initialization file. Response for the default filter has been
computed and is used to convert amplitude to ground motion. If other filter
parameters are used, the response must be calculated and used in the ground
motion calculations. The raw broadband data is still used, though, for Mwp
computations.
Two alarm features were added in this implementation of the Veith picker. This first
looks for potentially large quakes by comparing the signal amplitude at a
single station to a set threshold. The
amplitude threshold must be passed along with a duration threshold. When the amplitude threshold is surpassed
throughout the duration threshold in a cyclical manner, an alarm is declared
and fed to the alarm ring. Thresholds
are set in StaFile. A second alarm
feature was added in 2004. This alarm is
activated when strong P-arrivals are recorded at a specified number of stations
within a specified time period and distance range. Parameters for the second type of alarm are
set in the AlarmFile.
A no data alarm was also added to pick_wcatwc in 8/01. An alarm time is
specified in the .d file. If this time passes without data arriving in the
ring, an alarm message will be issued to the alarm ring. The picker attempts first motion
determination.
Graphical Interface:
This module has no graphical interface. Picks and some errors are logged
to the Windows console, if created.