West Coast/Alaska Tsunami Warning
Center
Operations Manual
NOAA/NWS/WCATWC
Palmer,
http://wcatwc.arh.noaa.gov
Section
4.1.15 – LOCATE
Last
Updated: 5/2006
Date Written:
11/1997
By: Whitmore
- WC/ATWC
Development Language: MicroSoft C/C++
v7.0
Initialization File:
locate.ini -
read on program start-up
Program Description:
Program LOCATE is a non-Earthworm-based program which runs independent of
any other seismic processing program.
Data files and semaphores are shared between LOCATE and other programs,
but it is not dependent on any other program.
Its main function is to interactively locate and size earthquakes based
on data obtained from loc_wcatwc/hypo_display or ANALYZE. (Though, P-picks and magnitude information
can be added through a menu option.)
Locations computed within this program are not forced or triggered by
any other module or program.
Locations are determined by a two-step process. First an initial guess is made at the
epicenter. This is either the location
of the station with the first P arrival, or a more sophisticated method using
station tripartites. Whichever type of initial locator is used, it produces the
starting point for an implementation of Geiger's location method. The location
are based on either the IASPEI91 travel times (Buland and Chapman, 1983;
Kennet, 1991) or the Jeffereys-Bullen travel times. The IASPEI91 P wave travel
times (Kennet, 1991) table was created using the
A routine was
added by Dave Nyland in 2006 which provides better depth control for
solutions. The quake depth is fixed to
the average depth for the region (based on NEIC historical data on a one degree
by one degree grid). When the location
is allowed to float, the depth will be limited by the maximum depth of the
region.
Program Controls:
A LOCATE screen display for a local Alaskan earthquake
is attached. On this figure, notice four buttons on the right side of the
screen named RT P's, Disk P's, RT LP, and Disk LP. These push buttons are used
to obtain data from lpproc, loc_wcatwc/hypo_display, and ANALYZE. The RT P's
button copies P-pick data, along with Mb, Ml, and Mwp magnitude information
from loc_wcatwc/hypo_display. The Disk P's button copies the same type of data
from ANALYZE. The RT LP button forces long period data processing to start (or
re-start) in lpproc and mm. The MS and Mw results are then copied into LOCATE.
Similarly, the Disk LP button forces long period data processing in ANALYZE and
the MS and Mw results are copied into LOCATE.
The three buttons below the LP buttons are used to
compute hypocenter solutions for the P data listed in the P-pick/magnitude list
box (left side of the screen). The Solve button forces a location using all the
P data which has not been eliminated from computations. Bad Ps also produces a
location given the P data, but it utilizes the bad P-pick discriminator to
remove up to three unassociated picks. The Use All button forces a location
using all P data in the list box including those which were previously
eliminated. The Depth Control buttons are used in solving hypocentral depth.
Initially the depth is set to the average for the region. The Float option is
used to let the PC solve for the depth which produces the lowest average
residual in the quake solution (constrained by the maximum for the region). The
Enter Below option allows a geophysicist to specify a depth based on pP-P times
or known information about the source zone. The Delete Station check box causes
a double-clicked P-time to be removed from the list when the box is checked.
The upper-right sections of the screen gives a short
summary of the last location produced by LOCATE. The large P-pick/magnitude
list box lists all P times to use in the solution. After the location has been
computed, residual, epicentral distance, azimuth, and magnitudes are listed for
each channel. At the bottom of the box, the average of each type of magnitude
is listed. (Modified averages are actually computed. That is, values
significantly different from the overall average are eliminated.)
The Add P/Mag menu item calls dialog boxes
which prompt for P-times and magnitude data to add to the P-pick/magnitude list
box.
Mouse buttons:
Left button double-click on station list eliminates
it from the computation (if Delete Station check box is clicked, the P is
deleted).
Menu Options:
Messages: Call program Message2 to create bulletin.
Alarm Print: Send alarm form to laser printer for
archive and records.
Locator:
Auto Initial:
(Default) First try locating earthquake using the station with the first
arrival time as the initial location. If
not a good solution, re-compute initial location with tripartite method.
Nearest Station: Use location of station with earliest P-arrival as initial location.
Compute Initial: Compute the initial location using the tripartite technique.
Fix Initial:
Take initial location from entry field on main screen.
Force Location: Set location for locator so that it will show residuals.
IASPEI91 Travel Times: When checked, use IASPEI91 travel times for
locations.
J/B Travel Times: When checked, use Jeffereys/Bullen P-time tables to compute locations.
Add P/Mag:
Add P-Time:
Enter a station/P-time.
Add Magnitude: Enter period/amplitude/gain information for magnitudes.
Options:
Print Location: Print last location on shared printer.
pP Depth:
Compute depth from pP-P time.
Compute Distances: Given two lat/lons, a distance between them will be output. Also, the geocentric lat/lon of point 1 will
be listed.
Voice:
Turn PC voice on/off.
Quake Summary File: Provide a file name and save the quake information to that file.
Locate on P Copy: Turn on/off location immediately after RT P’s or Disk P’s chosen.
Force Re-Process LP: Checked means that when RT LP or Disk LP are selected, the data in the
appropriate program is reprocessed for MS/MB.
Unchecked indicates just the MS/MB data files are copied over, the data
is not re-processed. This may be
necessary to uncheck when you have to get a magnitude by rubber-banding an MS
or MB cycle. This rubber-banded T/A will
be erased by the automatic re-processing of the LP data.
Seismo: (Used
for daily seismogram interpretations)
Add Comments: Add felt or tsunami information to a WC/ATWC
station with a P-pick.
Save Quake: Save P-data, comments, and hypocenter data for output
in daily files.
Send Seismo: E-mail SEISMO data to NEIC and others and log day’s
quakes to disk.
Delete
Seismo Files: Remove daily files for
start of next day’s records.
Refresh:
Re-paint the screen