Welcome to the second issue of the Southern California Earthquake Data Center's electronic newsletter. We produce this quarterly newsletter as part of our continuing efforts to make SCEDC data more accessible to our users, to improve our communication and outreach and to promote the tools and services we provide.
This newsletter will be archived at: www.data.scec.org/about/chronicle/. Please send your questions, comments, suggestions to: webmgr@quakedc.gps.caltech.edu.
Contents:
A. The Archive
B. Alternate Location Catalogs Available at the SCEDC
C. What's new with STP (Seismic Transfer Program)?
D. USArray - BigFoot
E. FAQ Highlight: Why do you have duplicate Catalog entries for some events?
F. SCEDC Advisory Committee
G. Development area on the SCEDC Website
The Archive: By the Numbers
Total size of the waveform archive: 3,047 GB
Size of SCEDC parametric and waveform database: 203,992,448 rows
For the period of Jan 1 - March 31, 2004 :
Data via transferred STP:
- 27,863,337 waveforms = average of 3.5 waveforms each second.
- 709 gigabytes of waveform data = average of 8,027 megabytes daily = 95 kilobytes per second.
The SCEDC archived:
- 3884 events
- 1,075,627 waveforms
- 67,900 arrivals
- 325,815 amplitudes
|
magnitude |
Number of |
|
0-1 |
767 |
|
1-2 |
1648 |
|
2-3 |
353 |
|
3-4 |
30 |
|
4-5 |
1 |
|
5-6 |
0 |
|
# of events |
event type |
|
2800 |
le (local event) |
|
176 |
qb (quarry blast) |
|
673 |
re (regional event) |
|
47 |
sn (sonic blast) |
|
2 |
st (subnet trigger) |
|
186 |
ts (teleseism) |
|
3884 |
TOTAL |
Continuous Archiving of High-Sample Rate Data
The SCEDC continuously archived 24 hours of HH_ (80 sps) and EH_ (100 sps) data from the entire array for the February 14th M 4.3 earthquake near Wheeler Ridge.
The mainshock and most of the larger aftershocks were preceded by small earthquakes by 5 to 10 seconds, which makes this sequence unique for studying earthquake triggering. Such triggering could be expected in, for instance, a Coso swarm, but is rarely observed in a mainshock-aftershock sequence like this one. The mainshock and its aftershocks were continuously archived for 2 hours prior to and 22 hours after the event.
More information on this topic is available at http://www.data.scec.org/about/sigeventsshot.html
B. Alternate Location Catalogs Available at the SCEDC
The Caltech/USGS southern California catalog archived and distributed by the SCEDC does not account for local variations in the seismic velocity structure, which limits the accuracy of our event locations. By applying various techniques in post-processing of the data, researchers have been able to improve location accuracy, and some of these improved catalogs are available at the SCEDC.
We have recently added two catalogs (Hauksson et al., 2004; Shearer et al., 2003) that use results from a SCEC-sponsored project that applies waveform cross-correlation to make precise differential times between nearby events. These times can then be used to greatly improve the relative location accuracy within clusters of similar events.
The following catalogs are available at the SCEDC at: http://www.data.scec.org/research/altcatalogs.html
Location Catalogs:
2004 - Hauksson, Chi and Shearer: locations using double-difference
2003 - Shearer, Hauksson, Lin and Klib: locations using waveform cross-correlation
2003 - Hauksson: 3-D earthquake locations
2000 - Richards-Dinger and Shearer: locations using source-specific station terms
Focal Mechanism Catalog:
2000 - Hauksson: 3-D earthquake focal mechanisms
Users can access location catalog files via our anonymous ftp site, or via the new "altloc" command in STP. The benefit of using STP to retrieve data is that it will let users search for events and allow comparison of locations between all four alternate location catalogs, as well as with the standard catalog (SCSN). For example, the following is the output of a request for all catalog entries for the Northridge earthquake:
STP altloc -e 3144585
3144585 1994/01/17,12:30:54.930 34.2012 -118.5477 18.28 6.70 w HAUK2003
3144585 1994/01/17,12:30:54.950 34.2023 -118.5396 19.70 6.70 w SHLK2003
3144585 1994/01/17,12:30:54.990 34.2207 -118.5502 16.33 6.70 w HAUK2004
3144585 1994/01/17,12:30:55.350 34.2076 -118.5438 17.03 6.70 w DS2000
3144585 1994/01/17,12:30:55.388 34.2130 -118.5370 18.40 6.70 w SCSN
# Number of events= 5
C. What's new with STP (Seismic Transfer Program)?
New STP Client - Version 1.4
We have recently released an updated version of our STP client. Version 1.4 fixes minor bugs and makes editline (line editing and command history functions) commands standard.
To get the new version:
- ftp scec.gps.caltech.edu
- login : ftp, password: your-email:address
- cd pub/programs/stp
- binary
- get stp1.4.tar
- quit
There is currently a UNIX and Linux client version, but we are considering developing clients for Windows or OSX if there is demand in the user community. If this is something that would be of interest to you, please let us know by emailing: mullaney@gps.caltech.edu.
"ALTLOC" Command
"ALTLOC" is a new command in STP that will allow searching and comparisons of the Caltech/USGS southern California catalog and four alternate location catalogs (see write-up above). For more information on this command, type "help altloc" from the STP command-line.
D. USArray - BigFoot
The transportable array component of USArray ("Bigfoot") formally began operation in California in January, 2004 and will stay until 2007. The southern California contribution to USArray includes the 39 currently-operating SCSN broadband stations listed below. The 40 sps BH_ data from these stations will be transmitted from the SCSN facility in Pasadena to both the Array Network Facility (ANF) and the IRIS Data Management Center (DMC) for archiving.
BigFoot is an excellent opportunity for the SCEDC to reach new users who are introduced to southern California seismic data through USArray. The Bigfoot array has a station-spacing of 70 km but the SCSN with its additional 115 stations has a mean station-spacing of around 50 km. Since the minimum depth to the Fresnel zone depends on the square of the station-spacing, data from the complete SCSN broadband array will allow researchers to image structures that are at about half the depth of the BigFoot array alone. This data from closely-spaced stations will be important for connecting upper-mantle structures to surface tectonic processes.
SCSN stations contributing to USArray:
ADO - Adelanto
BBR - Big Bear
BC3 - Big Chuckwalla
BEL - Bell Mountain
BFS - Mt Baldy Forest Service
CIA - Catalina Island
CWC - Cottonwood Creek
DAN - Danby
DEC - Green Verdugo
DVT - Desert View Tower
EDW - Edwards AFB
FMP - Fort MacCarthur
FUR - Furnace Creek
GLA - Glamis
GRA - Grapevine
GSC - Goldstone
HEC - Hector
IRM - Iron Mountain
ISA - Isabella
LGU - Laguna Peak
LRL - Laurel Mountain
MPM - Manuel Prospect Mine
MPP - McPherson Peak
NEE - Needles
OSI - Osito
PDM - Parker Dam
RCT - Rector
RRX - Barstow
SBC - Santa Barbara
SCI2 - San Clemente Island
SDP - Sudden Peak
SHO - Shoshone
SMM - Simmler
SNCC - San Nicholas Island
SWS - Superstition Mtn
TIN - Tinemeha
TUQ - Turquoise Mountain
VES - Vestal
WER - Wheeler Ridge
E. FAQ Highlight: Why do you have duplicate Catalog entries for some events?
Q: Why do you show two events in your catalog for the San Simeon event? Which one is correct, and which do you consider to be the SCEDC official San Simeon earthquake? Why is one listed as a teleseism, and one as a regional?
>From STP:
Event ID Type T0 Lat Long Depth Mag Mag Type
9966485 ts 2003/12/22,19:15:56.000 35.7000 -121.1000 8.00 6.50 w 0.0
9966449 re 2003/12/22,19:15:56.760 35.7085 -121.1043 7.01 6.54 l 0.5
# Number of events= 2
A: This is our standard operating procedure for large events. The San Simeon earthquake occurred in northern California, so it is considered a regional event for us in southern California. The magnitude/location solution that was calculated using our methodology at Caltech is the regional (re) solution and the teleseismic (ts) solution was supplied by the National Earthquake Information Center (NEIC). The authoritative solution for this event is the ts version which was provided to the NEIC by the Northern California Seismic Network and is available as a local event in the NCEDC catalog.
The waveforms associated with the ts version have a much longer time window than we typically archive for local events. For teleseismic events a distance-magnitude window is used to determine how much data to save. We archive 2000 seconds of waveform data for a M>=6 event at 30 degrees and 3000 seconds for M>=7 anywhere. For larger local events (M > 3.5), the entire array is recorded for ~200 seconds.
We would also have two versions if it were in our authoritative region e.g., the Northridge event has our local solution as well as a teleseismic version.
Northridge:
Event ID Type T0 Lat Long Depth Mag Mag Type
3144585 le 1994/01/17,12:30:55.388 34.2130 -118.5370 18.40 6.70 w 1.0
3140671 ts 1994/01/17,12:30:55.393 34.2160 -118.5380 17.36 6.70 s 1.0
# Number of events= 2
F. SCEDC Advisory Committee
In the fall of 2003, the SCEDC established an Advisory Committee consisting of representatives from the Data Center user community. The members of this committee are: Tim Ahern (IRIS), Ralph Archuleta (UCSB), Greg Beroza (Stanford), Robert Nigbor (USC), and John Vidale (UCLA). The establishment of this group allows for greater input by the scientific users in establishing and prioritizing Data Center goals and improving feedback methodology.
The SCEDC organized a town-hall meeting for the Advisory Committee and Data Center users at the 2003 SCEC Annual Meeting in Oxnard, CA. The Advisory Committee was asked to write a set of recommendations for the SCEDC on the issues presented in a self-report and any others brought up in the town-hall or Advisory Committee meetings. We asked that the recommendations address SCEDC priorities including science, data-management, operations and data-products.
This group delivered a report of their findings on October 1, 2003 which is published at: http://www.data.scec.org/about/advisory_report01.html
G. Development area on the SCEDC Website
From the SCEDC Research Tools page, there is a link to the Data Center's Development Page at http://www.data.scec.org/research_tools/development.html. This page contains links to SCEDC projects that are currently being developed and would benefit from testing by the user community. We are making these projects available to users to solicit feedback, but we also caution that these tools are under development.
Three of the projects available on this page are:
Clickable Map of Southern California Seismic Stations
Purpose: To show a map of currently-operating stations. Users can select stations for display by selecting from drop-down menus of channels and highlight specific stations. Users can click on stations and retrieve station information and continuous waveform data availability for individual channels. http://www.data.scec.org/network_maps/station.php
SeismiQuery
We are adapting IRIS's SeismiQuery for use on the SCEDC database. Our implementation of SeismiQuery is currently running off our development database and a few of the sections are not functional yet. You can watch our progress at http://www.data.scec.org/SeismiQuery.
Continuous Waveform Availability
Purpose: Allows a user to select a network/channel or an individual station/channel and graphically display what continuous waveform data is available in the SCEDC archive. The first display is a bar graph showing availability by year since 1999. Users can click on specific times on the graph and bring up a display showing a monthly breakdown and then click again to show a daily hour-by-hour breakdown. This tool is available at: http://www.data.scec.org/stations/search_net.php
