No abstract

Dynamic glacier activity is increasingly observed through passive seismic monitoring. We analysed near-regional-scale seismicity on the Arctic archipelago of Svalbard to identify seismic icequake signals and to study their spatialÁ temporal distribution within the 14-year period from 2000 until 2013. This is the first study that uses seismic data recorded on permanent broadband stations to detect and locate icequakes in different regions of Spitsbergen, the main island of the archipelago. A temporary local seismic network and direct observations of glacier calving and surging were used to identify icequake sources. We observed a high number of icequakes with clear spectral peaks between 1 and 8 Hz in different parts of Spitsbergen. Spatial clusters of icequakes could be associated with individual grounded tidewater glaciers and exhibited clear seasonal variability each year with more signals observed during the melt season. Locations at the termini of glaciers, and correlation with visual calving observations in situ at Kronebreen, a glacier in the Kongsfjorden region, show that these icequakes were caused dominantly by calving. Indirect evidence for glacier surging through increased calving seismicity was found in 2003 at Tunabreen, a glacier in central Spitsbergen. Another type of icequake was observed in the area of the Nathorstbreen glacier system. Seismic events occurred upstream of the glacier within a short time period between January and May 2009 during the initial phase of a major glacier surge. This study is the first step towards the generation and implementation of an operational seismic monitoring strategy for glacier dynamics in Svalbard.

Ð A program package, called HYPOSAT, has been under development that attempts to use the maximum information possible to estimate the hypocenter of a seismic source. The standard input parameters can be used: arrival times of ®rst and later onsets with backazimuths and ray parameters (or apparent velocities). In addition, travel-time dierences between dierent phases observed at the same station can be optionally used. The observed standard deviations are used to weight all input parameters and the inversion is done with a generalized matrix inversion code.A starting solution with a priori uncertainties can be calculated as the intersection of all backazimuth observations. If S observations are also available, a preliminary origin time is estimated using Wadati's approach to estimate a source time.Global earth models and user-de®ned horizontally layered local or regional models can be used alone or together to locate seismic events. To gain the best result from all input data, observations of all seismic phases as de®ned in the IASPEI91 tables can be inverted. Station corrections and corrections for phases with re¯ection points at the earth's surface can be applied by using local velocity structures.

International audienceThe goal of this study is to refine knowledge of the structure and tectonic history of the European Arctic using the combination of all available seismological surface wave data, including historical data that were not used before for this purpose. We demonstrate how the improved data coverage leads to better depth and spatial resolution of the seismological model and discovery of intriguing features of upper-mantle structure. To improve the surface wave data set in the European Arctic, we extensively searched for broad-band data from stations in the area from the beginning of the 1970s until 2005. We were able to retrieve surface wave observations from regional data archives in Norway, Finland, Denmark and Russia in addition to data from the data centres of IRIS and GEOFON. Rayleigh and Love wave group velocity measurements between 10 and 150 s period were combined with existing data provided by the University of Colorado at Boulder. This new data set was inverted for maps showing the 2-D group-velocity distribution of Love and Rayleigh waves for specific periods. Using Monte Carlo inversion, we constructed a new 3-D shear velocity model of the crust and upper mantle beneath the European Arctic which provides higher resolution and accuracy than previous models. A new crustal model of the Barents Sea and surrounding areas, published recently by a collaboration between the University of Oslo, NORSAR and the USGS, constrains the 3-D inversion of the surface wave data in the shallow lithosphere. The new 3-D model, BARMOD, reveals substantial variations in shear wave speeds in the upper mantle across the region with a nominal resolution of 1° × 1°. Of particular note are clarified images of the mantle expression of the continent-ocean transition in the Norwegian Sea and a deep, high wave speed lithospheric root beneath the Eastern Barents Sea, which presumably is the remnant of several Palaeozoic collisions

SUMMARY Teleseismic data have been collected with temporary seismograph stations on two profiles in southern Norway. Including the permanent arrays NORSAR and Hagfors the profiles are 400 and 500 km long and extend from the Atlantic coast across regions of high topography and the Oslo Rift. A total of 1071 teleseismic waveforms recorded by 24 temporary and 8 permanent stations are analysed. The depth‐migrated receiver functions show a well‐resolved Moho for both profiles with Moho depths that are generally accurate within ±2 km. For the northern profile across Jotunheimen we obtain Moho depths between 32 and 43 km (below sea level). On the southern profile across Hardangervidda, the Moho depths range from 29 km at the Atlantic coast to 41 km below the highland plateau. Generally the depth of Moho is close to or above 40 km beneath areas of high mean topography (>1 km), whereas in the Oslo Rift the crust locally thins down to 32 km. At the east end of the profiles we observe a deepening Moho beneath low topography. Beneath the highlands the obtained Moho depths are 4–5 km deeper than previous estimates. Our results are supported by the fact that west of the Oslo Rift a deep Moho correlates very well with low Bouguer gravity which also correlates well with high mean topography. The presented results reveal a ca. 10–12 km thick Airy‐type crustal root beneath the highlands of southern Norway, which leaves little room for additional buoyancy‐effects below Moho. These observations do not seem consistent with the mechanisms of substantial buoyancy presently suggested to explain a significant Cenozoic uplift widely believed to be the cause of the high topography in present‐day southern Norway.

We present a unique time series of continuous glacier frontal ablation rates with weekly resolution over 15 years estimated from seismic calving observations at Kronebreen, Svalbard. Using linear statistical models, we calibrate the seismic record with 7 years of satellite‐derived frontal ablation measurements. The two basic input parameters required for our models are the cumulative duration of individual seismic calving events and the incompleteness of the seismic record to correct for the effect of seismic background noise. Frontal ablation follows the seasonal glacier speedup, peaking 1–2 months after the melt season maximum. Short‐lived peaks are associated with melt and rain events. Cumulative frontal ablation of Kronebreen between 2001 and 2015 is about 4.0 km3 (3.7 Gt), with the greatest annual loss (0.45 km3) between 2013 and 2014 at the onset of the recent accelerated retreat of the glacier. Our approach provides a potential method for monitoring tidewater glaciers worldwide that have sufficiently close seismic instrumentation.

No abstract

No abstract