Location Program Released
The ISC announces the initial release of ISCloc, a program to compute hypocentres and magnitudes from phase arrivals times at a combination of local, regional and teleseismic distances.
ISCloc incorporates algorithms refined at the ISC over 35 years and used to compute published hypocentres for more than one million earthquakes. Consistency of ISCloc with the program used to date was confirmed by re-computing thousands of hypocentres and magnitudes. The new program was written to more readily use alternative travel time models, attenuation curves, and other parameters. A modular design allows users to introduce their own algorithms.
ISCloc uses Geiger's method to improve an initial hypocentre, and limits the effect of outliers with Jeffreys' uniform reduction algorithm. The program can automatically re-start iterations from different starting points until the solution converges.
ISCloc reads input data and writes results in ISF, the format recommended by IASPEI since 2001 for exchanging seismic bulletin data. ISCloc uses the ISF I/O library released in 2002, which the ISC intends to keep up to date with ISF amendments. Use of ISF means that the new version of WizMapII developed by the British Geological Survey in 2002 can be used as a graphical user interface to display maps of ISCloc results.
ISCloc has been tested at the ISC principally with Jeffreys-Bullen travel times, but the travel time models that are part of this release include iasp91 and ak135. The release includes P and S source and station corrections computed by the ISC from the Mooney-Laske 2° resolution global crustal model. ISCloc has also been tested with source-specific station corrections computed from laterally variable mantle models.
In a poster at IUGG, ISCloc developer Richard Luckett will describe results from his tests with several sets of travel time corrections. Somewhat surprisingly, he finds that corrections computed from crustal models improve neither seismically-determined hypocentres nor arrival time residuals for many events with ground-truth locations.
ISCloc is written in C, and the source code is available from the ISC web site at http://www.isc.ac.uk/doc/code/iscloc/. Full documentation can be consulted on-line at the same page.
Search for a New Director
The Executive Committee of the ISC Governing Council is searching for a new Director. The current Director, Ray Willemann, has told Council Chairman Adam Dziewonski that he plans to leave the ISC by the end of 2003.
The Committee encourages applications from candidates who have experience of data centre operations, preparing funding proposals, and managing a staff and budget. Knowledge of seismology and computing are both important.
Details of the application procedure are available from the ISC web site or can be requested from the ISC by phone, fax, post or e-mail. The Committee plans to accept applications until 1 June.
New FTP Service
ISC data files are now available from an anonymous ftp server with a broadband connection to the Internet. The server is physically remote from the Centre and can be accessed as seismo.gvon.co.uk. A link to the ftp server from the home page on ISC's web site can be used to download files from the ftp server with a web browser.
The service's main purpose is distributing complete results promptly when the ISC's final analysis for a month is done. Although this on-line distribution is much quicker than infrequently produced CDs, the ISC plans to continue distributing both the Catalogue CD and the Bulletin CD each year. The files for January to June 2001 are available already, and the ISC plans to post further files about once every four weeks.
Directories on the ftp site parallel those on ISC CDs. Catalogue files (which have only hypocentral parameters) and Bulletin files (with both hypocentres and associated phase readings) are available, and each is posted both in 96-column format and IASPEI Seismic Format (ISF). The files are compressed, which can greatly speed downloads even with the server's fast Internet connection. Even so, users who do not require phase data will still find that retrieving the Catalogue files is quicker.
The typeset monthly Bulletins and the semi-annual Regional Catalogues are also available as PDF documents. Users who browse the listings may find these typeset documents easier to use, and they include the separate lists of explosions and major events that have long been included in the Catalogue.
More Waveform Links
The ISC web site has been improved to help users of the on-line Bulletin retrieve waveforms from more data centres.
Some waveform data centres assemble sets of waveform segments for events of special interest, and for several years the On-line Bulletin has included hypertext links to such data sets. In addition, the ISC now provides a straightforward 3-step system to send e-mail requesting segments from continuous archives.
First the user selects an event and the system provides a summary of data available at the time of the event. Second, the user specifies parameters that control the channels and time intervals to be requested, and an e-mail address to which the waveforms should be sent. The system then lists the channels that satisfy the criteria. Third, the user removes unwanted channels and submits the list. The system then composes and despatches request messages to all of the data centres from which the user requires data, and posts a confirmation page to the user.
The system offers each user the choice of recording their channel and time interval criteria as a "cookie" in their web browser. A user who accepts the cookie can then compose requests for data for other events without re-entering the same criteria.
To be really useful, the service requires waveform inventories that are complete and accurate. The IRIS DMC and CMR provide services that enable the ISC to meet this challenge by retrieving channel lists in real time. For other centres, the ISC uses channel lists with station open and close dates and rules specific to some of the data centres regarding data availability.
The system supports both AutoDRM and BreqFast request protocols, and users receive e-mails with data in the default format for each data centre. The system already helps users retrieve data from several data centres in each of North America and Europe, and other data centres offering automated responses to e-mail requests for waveform data can be added quickly.
To try the system, users can select events from the On-line Bulletin and click on the waveform icon, which appears below each event line.
ISC Abstracts Posted
Members of the ISC staff plan to present several posters this year at the IUGG Assembly. Among other things, the posters will inform users about the ISC's new services, summarise recent results, and compare results with other bulletins.
Nurcan Özel and Dmitry Storchak will present a poster that compares coverage of Turkey in bulletins from the ISC and Kandilli Observatory. They conclude that outside of Kandilli's network, the ISC computes reliable hypocentres for more earthquakes using data from other agencies. Within the network, however, Kandilli's bulletin takes advantage of later phases as well as local travel times and attenuation models.
Another poster is on ISC's joint project with the University of Leeds to automatically measure SKS splitting. Matt Evans, a Leeds student, is first among authors from Leeds, the Czech Academy of Sciences, and the ISC. Matt plans for the poster to describe how he chose algorithms, partly by comparing results from several independently developed programs, as well as an initial set of measurements and their significance.
Interim Survey Results
For the past 4 months, the ISC has been asking web users of its on-line Bulletin to complete a simple survey. So far, 206 users in 47 countries have responded.
Respondents are asked to chose the one thing that is most important for ISC to do among "collect more data", "compute better hypocentres", or "improve data distribution". Of the 128 who answered this question, a small plurality favours a focus on collecting more data. Computing better hypocentres is the second favourite area for development. Only about 1 in 9 of all survey participants want the ISC to invest its efforts principally in improving distribution.
Among the 170 respondents who indicated what country they work in, the US (32) and Iran (13) are most well represented, followed by Greece, Russia, France, Canada, Romania and Japan. Among American respondents, more than half of those expressing a view think that the ISC should focus on data collection. Iranian, European Union and other respondents each agree with the Americans that data collection is most important. What's more, all of the geographically defined groups also agree that computing hypocentres is the next most important area for improvement.
Respondents were also asked to indicate in which fields of seismology they worked. Among those working in "earth structure", "explosion monitoring", "earthquake physics", "earthquake engineering" and "seismic hazard" the plurality view collecting more data as most important. Only among those in "tectonics" and "seismological methods" is computing better hypocentres the most popular area for improving the ISC. Perhaps the tectonicians emphasise hypocentral accuracy because they have the greatest need for it, regardless of how accuracy is achieved. On the other hand, many methodologists probably have strongly held views on just how ISC hypocentres should be improved.
The survey also asks about publications in refereed journals that make use of ISC data, which helps to demonstrate wide use of ISC services. Users who have not yet participated in the survey are encouraged to complete the form at http://www.isc.ac.uk/users/profile.htm and the follow-up form about publications using ISC data.