The 2007 seismological aftermath of the spreading episode of 1999 at Gakkel ridge, Arctic Ocean

In 1999, an unusually strong, teleseismically registered earthquake swarm at the volcanic complex at 85°E/85°N gave first signs of an ongoing spreading episode at Gakkel ridge, one of the World’s slowest spreading ridges (full spreading rate about 9mm/yr). Due to the remote location of Gakkel ridge in the ice covered Arctic ocean, an immediate on-site investigation was not possible. Following a first expedition to the 85°E/85°N volcanic complex in 2001, the 2007 AGAVE expedition recorded more than 300 local earthquakes during 21 days of recording with three arrays of seismometers mounted on ice floes. We localized the microearthquakes with the least-squares routine Hyposat and a local velocity model compiled from the nearest seismic surveys, and then identified reliable good quality events. These best events were used to test a suite of velocity models for the smallest overall rms and define the velocity structure in a 1D layered model for the 85°E/85°N volcanic complex. We localized the whole suite of local earthquakes with this velocity model. Most of the events were localized directly in the rift valley, though some epicentres extended as far as 88°E and had shallow hypocentres <10 km depth

Rebuild of the Bulletin of the International Seismological Centre (ISC), part 1: 1964–1979

Abstract The data from the Bulletin of the International Seismological Centre (ISC) have always been and still remain in demand for a wide range of studies in Geosciences. The unique features of the Bulletin include long-term coverage (1904-present), the most comprehensive set of included seismic data from the majority of permanent seismic networks at any given time in the history of instrumental recording (currently ~ 150) and homogeneity of the data and their representation. In order to preserve this homogeneity, the ISC has followed its own standard seismic event processing procedures that have not substantially changed until the early 2000s. Several considerable and necessary advancements in the ISC data collection and seismic event location procedures have created a need to rebuild the data for preceding years in line with the new procedures. Thus was set up a project to rebuild the ISC Bulletin for the period from the beginning of the ISC data till the end of data year 2010. The project is known as the Rebuild of the ISC Bulletin. From data month of January 2011, the ISC data have already been processed with the fully tested and established new procedures and do not require an alteration. It was inconceivable even to think about such a project for many tens of years, but great advances in computer power and increased support by the ISC Member-Institutions and Sponsors have given us a chance to perform this project. Having obtained a lot of experience on the way, we believe that within a few years the entire period of the ISC data will be reprocessed and extended for the entire period of instrumental seismological recordings from 1904 till present. The purpose of this article is to describe the work on reprocessing the ISC Bulletin data under the Rebuild project. We also announce the release of the rebuilt ISC Bulletin for the period 1964–1979 with all seismic events reprocessed and relocated in line with the modern ISC procedures, ~ 68,000 new events, 255 new stations, ~ 815,000 new seismic phases, more robust and reliable mb and M S magnitude evaluations and the addition of ~ 2700 new M S magnitudes