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

Last Updated: 9/2010

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
ResponseFile - Broadband instrument response in poles/zeroes format

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, alarming, and fine tuning the picks, but the main P-pick algorithm itself is very similar to that 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 are 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 sent 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.