In situ measurements of impact-induced pressure waves in sandstone targets

Abstract

In the present study we introduce an innovative method for the measurement of impact-induced pressure waves within geological materials. Impact experiments on dry and water-saturated sandstone targets were conducted at a velocity of 4600 m/s using 12 mm steel projectiles to investigate amplitudes, decay behavior, and speed of the waves propagating through the target material. For this purpose a special kind of piezoresistive sensor capable of recording transient stress pulses within solid brittle materials was developed and calibrated using a Split-Hopkinson pressure bar. Experimental impact parameters (projectile size and speed) were kept constant and yielded reproducible signal curves in terms of rise time and peak amplitudes. Pressure amplitudes decreased by 3 orders of magnitude within the first 250 mm (i.e., 42 projectile radii). The attenuation for water-saturated sandstone is higher compared to dry sandstone which is attributed to dissipation effects caused by relative motion between bulk material and interstitial water. The proportion of the impact energy radiated as seismic energy (seismic efficiency) is in the order of 10 À3 . The present study shows the feasibility of real-time measurements of waves caused by hypervelocity impacts on geological materials. Experiments of this kind lead to a better understanding of the processes in the crater subsurface during a hypervelocity impact.

Boulder stranding in ejecta launched by an impact generated seismic pulse

“…Low velocity laboratory impacts into granular media measure source times (as a half width) of about 10 µs (Yasui et al, 2015). Similar durations are measured in sandstone targets (Hoerth et al, 2014) and are predicted via numerical simulation (Güldemeister and Wünnemann, 2017). These pulse durations may be shorter than excited by astronomical impacts, as the seismic source time τ s could be longer for more energetic impacts (e.g., Lognonné et al 2009).…”

Experimental impact cratering: A summary of the major results of the MEMIN research unit

“…To determine the decay behavior of pressure amplitudes as a function of distance, a special type of piezo‐resistive sensor was developed and calibrated using a split Hopkinson pressure bar (Hoerth et al. ). Pressure amplitudes decreased by three orders of magnitude within the first 250 mm (i.e., 42 projectile radii).…”

“…The proportion of the impact energy radiated as seismic energy (seismic efficiency) was of the order of 10 −3 (Hoerth et al. ) in a sandstone target. Numerical modeling allowed for a more systematic investigation of the effect of porosity on seismic efficiency and the attenuation (quality factor Q) of seismic waves with distance.…”

Seismic Efficiency for Simple Crater Formation in the Martian Top Crust Analog

“…One way to estimate the detectability of an impact generated seismic signal is from the seismic efficiency, k , which quantifies the fraction of the impact energy that is partitioned into seismic energy (e.g., McGarr et al., 1969; Schultz & Gault, 1975). Estimates of seismic efficiency of impacts from a variety of studies vary widely from 10 ‐ 6 to 10 ‐ 1 (I. Daubar et al., 2018; Güldemeister & Wünnemann, 2017; Hoerth et al., 2014; Matsue et al., 2020; McGarr et al., 1969; Pomeroy, 1963; Richardson & Kedar, 2013; Schultz & Gault, 1975; Shishkin, 2007; Yasui et al., 2015). High seismic efficiencies ( k > 10 −3 ) are typically measured in explosions and nuclear tests in bedrock or highly consolidated materials (e.g., Patton & Walter, 1993), while low‐seismic efficiencies ( k < 10 −3 ) are seen in porous sediments or unconsolidated sands or soils (Latham et al., 1970; McGarr et al., 1969).…”