Fractures contribute to bulk elastic anisotropy of many materials in the Earth. This includes glaciers and ice sheets, whose fracture state controls the routing of water to the base and thus large-scale ice flow. Here we use anisotropy-induced shear wave splitting to characterize ice structure and probe subsurface water drainage beneath a seismometer network on an Alpine glacier. Shear wave splitting observations reveal diurnal variations in S-wave anisotropy up to 3%. Our modelling shows that when elevated by surface melt, subglacial water pressures induce englacial hydrofractures whose volume amounts to 1-2 percent of the probed ice mass. While subglacial water pressures decrease, these fractures close and no fracture-induced anisotropy variations are observed in the absence of meltwater. Consequently, fracture networks, which are known to dominate englacial water drainage, are highly dynamic and change their volumes by 90-180 % over subdaily time scales.

A precise velocity model is necessary to obtain reliable locations of microseismic events, which provide information about the effectiveness of the hydraulic stimulation. Seismic anisotropy plays an important role in microseismic event location by imposing the dependency between wave velocities and its propagation direction. Building an anisotropic velocity model which accounts for that effect allows for more accurate location of microseismic events. We utilize downhole microseismic records from a pilot hydraulic fracturing experiment in Lower-Paleozoic shale gas play in Baltic basin, Northern Poland to obtain accurate microseismic events locations. In this paper we develop a workflow for a VTI (i.e. vertical transverse isotropy) velocity model construction when facing a challenging absence of horizontally polarized S-waves in perforation shots data, which carry information about Thomsen’s γ parameter and provide valuable constraints for location of microseismic events. We extract effective ε, δ and V_P0, V_S0 for each layer from P- and SV-waves arrivals of perforation shots, while the unresolved γ is retrieved afterwards from SH-SV-waves delay time of selected microseismic events. Inverted velocity model provides more reliable location of microseismic events which then becomes an essential input for evaluating the hydraulic stimulation job effectiveness in the geomechanical context. We discuss the influence of the pre-existing fracture sets and obliquity between the borehole trajectory and principal horizontal stress direction on the hydraulic treatment performance. The fracturing fluid migrates to previously fractured zones, while the growth of the Microseismic Volume in consecutive stages is caused by increased penetration of the above-lying lithological formations.

Observations of azimuthal seismic anisotropy provide useful information, notably on stress orientation and the presence of pre-existing natural fracture systems, during hydraulic fracturing operations. Seismic anisotropy can be observed through the measurement of shear-wave splitting (SWS) on waveforms generated by microseismic events and recorded on downhole geophone arrays. In this paper we present measurements of azimuthal anisotropy from a Lower Paleozoic shale play in northern Poland. The observed orthorhombic anisotropic symmetry system is dominated by a vertically-transverse isotropy (VTI) fabric, produced both by the alignment of anisotropic platy clay minerals and by thin horizontal layering, and overprinted by a weak azimuthal anisotropy. Despite the dominating VTI fabric, we successfully identify a weaker HTI fabric striking east-southeast. We do this by constraining the rock-physics model inversion with VTI background parameters incorporated from other geophysical methods: microseismic velocity model inversion, 3D reflection seismic and borehole cross-dipole sonic logs. The obtained orientation is consistent with a pre-existing natural fracture set that has been observed using XRMI image logs from a nearby vertical well. The present-day regional maximum horizontal stress direction differs from the observed fracture strike by approximately 45^°. This implies that the SWS measurements recorded during hydraulic stimulation of shale gas reservoir are imaging the pre-existing natural fracture set which influences the treatment efficiency, instead of the present-day stress.

Retreating glaciers are a consequence of a warming climate. Thus, numerous monitoring campaigns are being carried out to increase understanding of this on-going process. One phenomenon related to dynamic glacial changes is glacier-induced seismicity; however, weak seismic events are difficult to record due to the sparse seismological network in arctic areas. We have developed an automatic procedure capable of detecting glacier-induced seismic events using records from a single permanent seismological station. To distinguish between glacial and non-glacial signals, we developed a fuzzy logic algorithm based on the signal frequency and energy flow analysis. We studied the long-term changes in glacier-induced seismicity in Hornsund (southern Spitsbergen) and in Kongsfjorden (western Spitsbergen). We found that the number of detected glacial-origin events in the Hornsund dataset over the years 2013-14 has doubled. In the Kongsfjorden dataset, we observed a steady increase in the number of glacier-induced events with each year. We also observed that the seasonal event distribution correlates best with 1 month lagged temperatures, and that extreme rain events can intensify seismic emissions. Our study demonstrates the possibility of using long-term seismological observations from a single permanent station to automatically monitor the dynamic activity of nearby glaciers and retrieve its characteristic features.

Glacier ice flux is a key indicator of mass balance; therefore, accurate monitoring of ice dynamics is essential. Satellite-based methods are widely used for glacier velocity measurements but are limited by satellite revisit frequency. This study explores using seismic station internal GPS data to track glacier movement. While less accurate than differential GPS, this method offers high-temporal resolution as a by-product where seismic stations are deployed. Using a seismic station on Borebreen, Svalbard, we show that internal GPS provides reliable surface velocity measurements. When compared with satellite-inferred velocities, the results show a strong correlation, suggesting that the internal GPS, despite its inherent uncertainty, can serve as an efficient tool for glacier velocity monitoring. The high-temporal sampling reveals short-term dynamics of speed-up events and underscores the role of meltwater in driving these processes. This approach augments glacier observation networks at no additional cost.