July - September 2002

Contents

New Seismologist at the ISC
National Science Foundation Renews Funding
Visitors to the ISC
Further Special Data
E-mail Bulletin Subscriptions now Available
Shear Wave Splitting Project Gets Underway

New Seismologist at the ISC

Nurcan Meral Özel joined the ISC in August to help edit results from automatic processing in preparing the Bulletin. Editing had been shared by just Dmitry Storchak and Mamy Andrianirinna since January, when Melda Banganan returned to the Philippines. Regular change among the editors helps to fulfil the ISC's mandate to promote international exchange of seismological expertise.

While at the ISC, Nurcan is on leave from the Kandilli Seismic Observatory and ERI, Bogazici University, Istanbul. Nurcan started at Kandilli in 1984 and earned her MSc there with a thesis on earthquake risk models. She has comprehensive experience at Kandilli helping to prepare its national seismic bulletin.

Kandilli Observatory had to make do without Nurcan once before, from 1991 to 1995, while she earned her PhD at the Univ. of Hokkaido with Prof. Hiroshi Okada. In collaboration with Takeo Moriya and Tsutomu Sasatani at Hokkaido, Nurcan used local and regional data to determine earthquake source mechanisms, and then to compute regional stress patterns.

After returning to Turkey, Nurcan joined in Kandilli Observatory's intensive work that followed major earthquakes in 1999 near Izmit and Düzce.

Nurcan says that she was attracted to the ISC by the opportunity to contribute to a Bulletin that is used by seismologists all around the world. All of us at the ISC hope that Nurcan's idealism survives the British weather, which she tells us is somewhat different to Turkey's.

National Science Foundation Renews Funding

Continuing an ongoing associa-tion, the US National Science Founda-tion has awarded a new grant that will provide about 20% of financial support for ISC operations over the next four years.

The ISC is committed to collecting data from earth-quake bulletins published during the grant period and distributing results from its own re-analysis for earthquakes over 48 months. New to this grant, the ISC has promised to continue making data from the Bulletin back to 1964 readily available on its web site and AutoDRM e-mail server.

In addition to partial support of operations, the grant includes full support for an extra staff member for two years to re-write the ISC earth-quake location program. The new program is meant to adapt readily to different travel times, algorithms, and station networks thanks to a modern modular design.

ISC seismologists could use the new program for interactive trial re-locations. The ISC also plans to use the new program to support on-line re-location of events with subsets of ISC phases or alternative travel-times.

Visitors to the ISC

The ISC has welcomed visitors to the ISC regularly over the last few months.

Bob Engdahl of the Univ. of Colorado reviewed integration of his re-identified phases and re-computed hypocentres into the ISC database. Bob addressed questions about stations and confirmed that EHB data available from the ISC are a faithful copy of his catalogue.

Bruce Bolt of the Univ. of California described the COSMOS strong motion data programme. Bruce reviewed links to the COSMOS Virtual Data Center in ISC's On-line Bulletin and suggested how best to keep these links up to date.

Avi Shapira of the Geophysical Institute of Israel looked at ISC integration of GII regional events with other catalogues. Since Avi's visit, GII has started to contribute teleseismic readings to the ISC, in addition to its regional catalogue.

Bob Blandford of the US Air Force learned how to obtain readings that were reported to the ISC but not associated with any event in the Bulletin. Bob may be able to associate these readings with events in other catalogues.

Paul Denton of the Univ. of Leicester described SEIS-UK, which supports a pool of portable seismometers. We started to plan for integrating SEIS-UK arrival measurements and event parameters in the ISC database.

Bill Walter of the Lawrence-Livermore US National Laboratory described new methods to compute reliable magnitudes from regional waves. We discussed the possibility of calibrating attenuation near some stations that report to the ISC.

Professors Huo Enjie, Zhu Yuanqing, and Fan Changqing of the Shanghai Seismological Bureau described their broadband array and 16-station network, which help to locate earthquakes all across southeastern Asia. Director Huo Enjie plans to consider contributing both phase readings from his network and SSB hypocentral parameters to the ISC.


Bob Engdahl

Bruce Bolt

Bob Blandford

Bill Walter

Further Special Data

The ISC's collection of catalogues from temporary deployments and other special studies has grown substantially since its start early this year.

Bob Urhammer contributed events and associated arrival times from the PASSCAL experiment SAPSE in New Zealand, and Donna Eberhart-Phillips offered help in parsing the data. Stacey Robertson and Doug Wiens contributed hypocentres near the Antarctic Peninsula from the PASSCAL experiment SEPA. Stacey computed the SEPA hypocentres partly from arrival times at OBS stations deployed by Leroy Dorman. As with other PASSCAL experiments, in the On-line Bulletin each SAPSE and SEPA event includes a link to retrieve related waveform data from the IRIS DMC.

OBS sites, land stations on the Antarctic peninsula, and earthquake hypocentres from “SEPA”.

The SEPA data were not the first OBS arrival times at the ISC, thanks to Cliff Frohlich's earlier contribution of an OBS-based catalogue of earthquakes near Efate Island, Vanuatu. Doug Wiens may also contribute OBS arrival times from SPASE, a PASSCAL experiment near Fiji. The ISC has talked with members of the OBS-IP programme board about routinely contributing of catalogues from experiments that use their instruments. The ISC hopes to make similar arrangements with other programmes that provide instruments for different projects over time, such as PASSCAL, SEIS-UK and the German Task Force for Earthquakes.

Catalogues of aftershocks from major earthquakes are often produced urgently, and sometimes they are contributed quickly enough to be included in the ISC's own analysis in preparing the Bulletin. The ISC has already received a catalogue of aftershocks of the 2001 January earthquake near Bhuj from Hiroaki Negishi and Tamao Sato at Hirosaki University. We also hope to receive another catalogue of Bhuj aftershocks from Paul Bodin at Memphis State University.


Jochen Braunmiller has contributed moment tensor solutions for European-Mediterranean earthquakes that are computed from regional arrivals. These complement regional centroid-moment tensor solutions from near-real time data by Günter Bock of GFZ Potsdam and from MedNet data by Andrea Morelli and Silvia Pondrelli of INGV Rome. "Beach ball" figures in the On-line Bulletin make it easy to compare the moment tensor solutions computed using different techniques and data.


Harvard
MW=5.3
h=15km


INGV, Rome
MW=5.2
h=15km


SED, Zurich
MW=5.5
h=30km

Moment tensors in the on-line Bulletin for a strike-slip earthqauke on the North Anatolian fault in 2000 August are similar despite large CLVD components.

E-mail Bulletin Subscriptions now Available

The ISC has created a system for subscribing to monthly releases of user-selected data from the Bulletin. The system lets anybody with e-mail receive results for earthquakes in regions of interest to them as soon as the ISC completes its final analysis.

The ISC has used Urs Kradolfer’s Automated Data Request Manager (AutoDRM) to fulfil e-mail data requests since 2000. The subscriptions use the same system, but allow users to create standing orders for further data as ISC finishes its analysis for each month.

To subscribe, users need only send a “subscription” AutoDRM message to autodrm@isc.ac.uk. The ISC posts advice on composing AutoDRM “request” and “subscription” messages at http://www.isc.ac.uk/doc/autodrm/. Or users can send this message:

BEGIN GSE2.0
EMAIL user@site.domain
HELP
STOP

to autodrm@isc.ac.uk after replacing user@site.domain with their own e-mail address.

Shear Wave Splitting Project Gets Underway

The University of Leeds has undertaken a project to automatically measure shear wave splitting. The project is being carried out in close collaboration with the ISC in order to ensure that the new measurements continue to be made and included in the Bulletin after the project concludes. Funding from the UK Natural Environment Research Council includes partial support for ISC staff members helping to integrate the measurements into the ISC database.

Leeds Professor Mike Kendall is the project's principal investigator, but Matt Evans will carry out much of the work. Matt is a Leeds PhD student who has worked at the ISC before. In his earlier stint at the ISC Matt developed software to retrieve waveform segments at the expected times of phases from selected earthquakes.

Matt's waveform retrieval software will be part of the splitting measurement system. When waveforms are received at the ISC, the system will automatically measure splitting and its reliability, then save the results in the ISC database. When users select arrivals from the on-line Bulletin, the splitting measurements will be included. A new web page could help users formulate queries for particular splitting measurements.

Matt Evans is working at the ISC again, this time as part of a collaboration with the University of Leeds.

Mike Kendall visited the ISC to set the project off to a good start and talk with ISC staff members about the purpose of splitting measurements. Splitting of teleseismic shear waves reveals mantle anisotropy, which results from alignment of crystals by deformation in the past.

Collections of splitting measurements are already available from several individual researchers. But where measurements are inconsistent with simple anisotropy it may be unclear whether the conflict arises from complex anisotropy or differences between the measurement methods. This project is intended to resolve such questions by using a consistent method to make many more measurements than have been made in individual studies.

The project will also highlight general issues about measurements from widely available digital waveform data. Such measurements are not necessarily made by network operators and should be repeatable. Nevertheless, archiving and re-distributing generally accepted measurements might be useful to other researchers who prefer to interpret the past rather than repeat it.