Elastic properties as indicators of heat flux into cold near-surface Arctic sediments

Abstract

Temperatures in the terrestrial Arctic are today increasing at the highest rate on Earth, and heat flux into the cold sediments may result in extensive thawing. Thawing sediments lose their mechanical strength, and warming therefore has significant geomorphic consequences. We have combined heat flux, rock physics, and seismic modeling to estimate the change in elastic properties related to various published future climate scenarios in the Arctic, and thus investigate the feasibility of exposing thawing rates from seismic data. The heat-flux model was validated using temperature data continuously recorded at the surface and within a well in Adventdalen, Svalbard. We estimated the evolving temperatures in an upper vertical section of the well using the heat-flux model, and compared with actual measured well temperatures. The modeled and measured data were consistent, even though our simplified model ignores heat transport due to fluid flow and the effects of clay. The heat flux modeling resulted in subsurface isotherms that were input to rock physics modeling based on two-end-member mixing of fully frozen and unfrozen composites to delineate possible climate effects on the seismic properties of the sediments. The results show that elastic and seismic properties of (partly) frozen unconsolidated near-surface saline sediments strongly depend on heat flux into the subsurface, and vary both seasonally and between different climate scenarios. Seismic data obtained by full waveform modeling and real experiments in Adventdalen show that time-lapse analysis of Rayleigh waves may be an efficient tool for monitoring heat flux into the terrestrial Arctic.

Potential Use of Time-Lapse Surface Seismics for Monitoring Thawing of the Terrestrial Arctic

“…Combining the resulting velocities with Equation 1, we can determine how seismic velocities vary with time and depth. The complete approach of combing heat flux modeling, rock physics modeling, and the equations for seismic velocities to investigate how seismic velocities vary with time is described in detail in [35]. Figure 2 shows the result of using this approach on high-porosity sand with high-salinity pore water, considering scenarios T1, T2, and T3 (solid lines in Figure 1a).…”