Data Services Newsletter

Volume 2 : No 3 : September 2000

The University of Washington

The University of Washington is the host institution for the IRIS Data Management Center. As host institution, we provide a high speed link to the internet, several value-added projects and access to good coffee. In particular, we developed and maintain the SPYDER® System, provide a variety of waveform and software quality control functions, pick travel times, aid in the development and testing of products and software such as the FARM, WEED and breq_fast, and analyze noise at broadband GSN stations.

SPYDER®

A description of the SPYDER® System can be found in this newsletter.

Software and Waveform Quality Control

We have worked closely with DMC staff at the initial design, systematic testing, and upgrade stages for breq_fast, FARM and WEED. Periodically, these products are systematically tested. Feedback is provided to DMC staff on suggestions to improve functionality and on options that do not work as documented. We also have done extensive testing of rdseed, especially in regard to instrument responses and evalresp. We wrote and maintain code to plot the record sections for FARM and SPYDER® events which are viewable through WILBER.

We periodically and systematically check the quality of waveform data in several ways. Clocks are checked by picking P-wave travel times and analyzing their residuals as a function of event date to look for drifts. Errors in excess of 1-2 s are found in this way and reported to the DMC through Data Problem Reports (DPRs) and semi-annual reports. Gain on each GSN station is systematically checked by comparing long-period amplitudes of P waves of FARM events. Errors in excess of a few 10s of percent can be found in this way. Polarity of long-period P and SH are systematically checked. We use data from the DMC archives, standard request mechanisms and RDSEED so we test the data as they are distributed to the user community. This process uncovers software and data archiving bugs as well as problems with metadata and time series.

Travel-Time and Amplitude Picking

Recently, the DMSSC recommended that the DMS be responsible for routine picking of travel times from IRIS stations, both as a quality control function and to produce a valuable catalog. As a result, the IRIS/USGS and the IRIS/IDA Data Collection Centers as well as our own group have recently begun active picking projects. The DCCs generally pick times from their own stations as the data comes in from the field. Our efforts are complementary in that we also pick times from older earthquakes and PASSCAL experiments. There is some duplication of effort which allows us to compare our picks with the IRIS/USGS picks. Our picks generally agree to within 1 s.

We routinely pick travel times and amplitudes of P and PKP phases of broadband seismograms in the IRIS FARM. To date we have picked all the P waves for the 1995 through 1999 FARM, and P and PKP data for one PASSCAL experiment. These times are analyzed by station to look for station problems. They are sent to the ISC, to Dr. Robert Engdahl for incorporation in his widely distributed compilation of travel times and earthquake locations, and are available on our web site. Plans for the future include picking times from 1977-1994 FARM events as well as data from the new FARM (see article in this newsletter), which will include many more networks, stations and events. Differential travel times of various phases that we use for our own research are also distributed on this web page, as well as an analysis comparing our picks to those of other groups and picks from broadband records versus narrow-band, short-period records.

Noise Study

A comprehensive study of broadband seismic noise at GSN stations was conducted at the UW by Luciana Astiz (see FDSN Station Book). We applied a robust method to a large volume of waveform data recorded at over 100 three-component, broadband stations covering nearly five orders of magnitude in frequency. The code has been distributed to groups around the globe who are following this methodology.

by Kenneth Creager (University of Washington)

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