Description: The GLATIS project (Greenland Lithosphere Analysed Teleseismically on the Ice Sheet) with collaborators has operated a total of 16 temporary broadband seismographs for periods from 3 months to 2 years distributed over much of Greenland from late 1999 to the present. The very first results are presented in this paper, where receiver-function analysis has been used to map the depth to Moho in a large region where crustal thicknesses were previously completely unknown. The results suggest that the Proterozoic part of central Greenland consists of two distinct blocks with different depths to Moho. North of the Archean core in southern Greenland is a zone of very thick Proterozoic crust with an average depth to Moho close to 48 km. Further to the north the Proterozoic crust thins to 37–42 km. We suggest that the boundary between thick and thin crust forms the boundary between the geologically defined Nagssugtoqidian and Rinkian mobile belts, which thus can be viewed as two blocks, based on the large difference in depth to Moho (over 6 km). Depth to Moho on the Archean crust is around 40 km. Four of the stations are placed in the interior of Greenland on the ice sheet, where we find the data quality excellent, but receiver-function analyses are complicated by strong converted phases generated at the base of the ice sheet, which in some places is more than 3 km thick.

Description: Within Project Tor, which is about Teleseismic Tomography across the Tornquist Zone in Germany–Denmark–Sweden, we have confirmed very significant deep lithosphere differences. And modeling is substantiated via completely independent methods. In 1996–1997 our 130 seismographs constituted the largest seismic antenna ever in Europe. The Tor area was chosen along a well studied crustal profile of an earlier project, and the modeling efforts were concentrated on the deep lithosphere and asthenosphere differences to depths around 300 km. The Tor data have been subjected to P-wave travel time tomography, surface wave and receiver function analysis as well as anisotropy and scattering measurements. An important goal of the project was to make several independent inversions of the tomography data, and compare the results in an attempt to evaluate uniqueness, resolution and accuracy of these inversions. The comparisons of this paper involve more diversity in methods than any previous comparison. The geological outcome is a substantiation of earlier statements that: “The transition is interpreted to be sharp and steep in two places. It goes all through the lithosphere at the northern rim of the Tornquist Zone near the border between Sweden and Denmark, and here the lithosphere difference is large to depths more than 200 km. The other lithosphere difference, of smaller scale, is found near the southern edge of the Ringkøbing-Fyn High near the border between Denmark and Germany. Also this transition is sharp and steep, and goes all through the lithosphere to depths around 120 km. These two sharp transitions divide the Tor region into 3 different lithosphere structures distinguishable in P-wave travel time tomography, surface wave dispersion, P- and S-wave anisotropy and partly in P-wave scattering”. The mentioned broad-scale features are judged to be unambiguously determined, with well-described resolution and accuracy. Unfortunately a detail like the slope of the subcrustal lithosphere transition right under the Tornquist Zone cannot be constrained even if this is where the resolution is best, and the curiosity largest.

Description: The dynamics of the large outlet glaciers in Greenland is attracting both scientific and political attention due to the possible implications of a rising global sea level. Extensive glaciological and meteorological monitoring programmes have been implemented to quantify and track changes in the ice sheet and local glaciers (Ahlstrøm et al. 2008). The dynamic processes controlling the flow of the outlet glaciers are complex and poorly understood, involving a wealth of parameters such as bed conditions, hydrology and meteoro-logical conditions. It is desirable to obtain as many funda-mentally independent data sets as possible to understand and eventually predict the behaviour of the outlet glaciers. Some processes related to ice dynamics can be detected seismologically and thus completely independently from classical ice-monitoring techniques, such as satellite remote sensing, global positioning system (GPS) geodesy and auto-matic weather stations. Detectable cryo-seismological events include high-frequency ice quakes (Anandakrishnan & Bent-ley 1993; Harrison et al. 1993), calving events (O'Neel et al. 2006; Nettles et al. 2008) and less well understood processes such as low-frequency glacial earthquakes (Ekstrom et al. 2003; Nettles et al. 2008)) and glacial rumblings (Rial et al. 2009). Changes in ice load along the margin of the ice sheet can lead to earthquakes from glacial rebound, and earth-quakes can provide an independent constraint on ice mass redistribution (Johnston 1987; Stewart et al. 2000; Lund & Näslund 2009). The Greenland ice sheet monitoring network (GLISN) project will monitor changes in glacier dynamics using a large broadband seismological network. The network will also improve the detection of tectonic earthquakes in Green-land, thereby establishing a better baseline for local seismi-city. The baseline will allow detection of future changes in seismicity caused by changes in ice load. It is the objective of the project to contribute significantly to understanding the dynamics of the Greenland ice sheet and glaciers by studying cryo-seismological processes. Installing and operating a large real-time seismological network in Greenland is logistically complicated and expen-sive. An international team consisting of researchers from 10 institutions in 8 countries in Europe, North America and Asia are working together to meet this challenge (Fig. 1). Glacial earthquakes and rumblings Cryo-seismological events such as glacial earthquakes and rumblings can be linked to large-scale glacier dynamics. Gla-cial earthquakes are produced at large outlet glaciers and ap-pear to be associated with large calving events (Amundson et al. 2008; Nettles et al. 2008). However, the processes leading the GLISN group Fig. 1. Map of broadband seismographs in Greenland. 1–4: permanent stations operated by GEUS in cooperation with other institutions. 5–7: long-term stations maintained by GEUS. 8–9: new GLISN long-term stations run by ETH (Switzerland). 10: a long-term station run by GEO-FON (Germany). 11: a permanent station at Alert in Canada run by IRIS (USA). 12: a temporary station run by GEUS. 13–18: planned and funded new GLISN stations to be installed by IRIS and ETH.

Description: The SEISAN Earthquake Analysis Software is used widely at regional, national and local seismic networks and by students and researchers in the field of seismology. SEISAN is applied in the monitoring of all kinds of seismic events: Earthquakes, volcanoes, induced and cryo-generated events. SEISAN provides many different programs, from the basic processing and analysis of seismic events at seismological observatories to more advanced research. Based on a flat file database structure it operates on all platforms. SEISAN has undergone steady development since its launch more than 30 years ago. The design and development of SEISAN is and has been conducted in close contact with end users, to ensure fast and efficient workflows. SEISAN includes a comprehensive manual, a tutorial, training exercises and a mailing list where users and experts share information and help each other. SEISAN workshops have been held regularly since the nineties and have in the recent years been supplemented with online web sessions. To the CTBTO national data centres, SEISAN applications are presented at the forum web site. The recent improvements to SEISAN include QuakeML routines for data exchange, near real time event detection and processing and full channel identification and logging of event processing. References: Havskov, J., Voss, P.H. and Ottemoller, L. (2020). Seismological Observatory Software: 30 Yr of SEISAN. Seismological Research Letters, 91 (3): 1846-1852. DOI: https://doi.org/10.1785/0220190313 Ottemöller, L., Voss, P.H. and Havskov J. (2021). SEISAN Earthquake Analysis Software for Windows, Solaris, Linux and Macosx, Version 12.0. 607 pp. University of Bergen. ISBN 978-82-8088-501-2, http://seisan.info