During the IUGG General Assembly, 1999, Birmingham, UK, a IASPEI Working Group has been formed with the objective of collecting and validating reference events located with 5km accuracy or better. The members of the Working Group are
Accurate locations are crucial in testing Earth models derived from body and surface wave tomography as well as in location calibration studies. Kennett and Engdahl, 1991, used a suite of well-located events to set the baseline and validate the IASP91 travel time tables. The ISC groomed data set (Engdahl et al., 1998) contains events located with 15 km accuracy or better in most continental areas. The nuclear explosion (Yang et al., 2000a) and ground truth event databases (Yang et al., 2000b) maintained at the Prototype International Data Center, Arlington, VA, USA, contain information on nuclear explosions carried out since 1945 and natural and man-made events located with 0-25 km accuracy.
Several groups have been working on classifications and protocols for validating reference events, including Bondár et al., 2001 and the CTBTO Calibration Program. The IASPEI Working Group on Reference Events has adopted guidelines which are consistent with these programs, but taken in a broader scientific context (e.g., development and testing of three-dimensional Earth models).
In regional location calibration where the expected improvements due to better travel time predictions are on the order of 5-10 km, events used in the validation of the travel time corrections have to be known with at least 5 km accuracy (GT5). The location and depth of events in the GT0 category are exactly known; these are mostly nuclear explosions, calibration explosions or large chemical shots of refraction profiles. Category GT2 are events with location accuracy better than 2 km. GT2 events include mine explosions and quarry blasts where the event can be tied to a known mine or quarry location and the diameter of the mine does not exceed 2 km. Locations obtained from space imagery may also fall into this category. GT5 events are mostly local network locations of events occurring inside the network or from temporary aftershock deployments. As a guideline we developed criteria similar to those of Dewey et al., 2000 for events that can most likely be accepted as GT5.
GT5 candidate event selection criteria at the 90% confidence level
GT5 candidate event selection criteria at the 95% confidence level
where secondary azimuthal gap is defined as the largest azimuthal gap a station closes.
It should be noted that the origin time and depth of reference events might still be poorly constrained, both for natural and explosive sources even when these GT5 criteria are met. Nevertheless, accuracy of origin time and depth is an extremely important consideration for inclusion in the Reference Event List.
The seismological community is invited to participate in this project by providing reference event information. Submitters may be contacted for further confirmation and for arrival time data by the Working Group Chair. The IASPEI Reference Event List will be periodically published both in written and electronic form with proper acknowledgement of all submitters. A Working Group meeting and poster presentation are planned at the Joint IAGA/IASPEI Scientific Assembly to be held in Hanoi, Vietnam, during the period 20-31 August 2001. For further particulars link to .
The first version of the Reference Event List is posted on the web. Please note that this list is subject to change and it is considered a 'beta' version. The finalized IASPEI Reference Event List 1.0 is anticipated to be released by the end of this year. Download beta version of the IASPEI Reference Event List 1.0.
Bondár, I., X. Yang, R.G. North and C. Romney, Location
Calibration Data for CTBT Monitoring at the Prototype International Data
Center, Pageoph, 158, 19-34, 2001.
Dewey, J. W., E. Herron and J.O. Kork, Recent calibration
events in the United States, CTBT/WGB-11/US/1, 2000.
Engdahl, E.R., Van der Hilst, R.D., and Buland, R.P.,
Global teleseismic earthquake relocation with improved travel times and
procedures for depth determination, Bull. Seism. Soc. Am. 88,
722-743., 1998.
Kennett, B.L.N. and E.R. Engdahl, Traveltimes for global
earthquake location and phase identification, Geophys. J. Int. 105,
429-465, 1991.
Terms of Reference,
CTBTO/IDC Calibration Programme, Phase 1, March 2000
Yang, X., R. North and C. Romney, CMR Nuclear Explosion
Database (Revision 3), Center for Monitoring Research CMR-00/16,
2000a.
Yang, X., I. Bondár and C. Romney, PIDC Ground Truth Event
(GT) Database (Revision 1), Center for Monitoring Research CMR-00/15,
2000b.