The role of regolith thickness in seismic shaking on asteroids

<p>Near-Earth Asteroids visited by spacecraft display a depletion in the number of small craters (< 100 m). For example, the fractured monolith 433 Eros (Thomas et al., 2005), and the rubble piles 25143 Itokawa (Michel et al., 2009), 162173 Ryugu (Noguchi et al., 2021), and 101955 Bennu (Daly et al., 2020) all show a depletion in small craters. Models of the crater populations on Eros and Itokawa indicate that the depletion can be explained by seismic shaking induced by meteorite impacts (e.g., Thomas et al., 2005; Richardson et al., 2004; 2005; Michel et al., 2009). The effects of seismic activity occur in the active layer, the uppermost layer of the regolith. Previous models of seismic shaking that recreate crater populations have used a broad range of active layer depths, ranging from 0.1 m to 5 m across various models for Itokawa and Eros (Richardson et al., 2004; 2005; 2020; Michel et al 2009; Susorney et al., 2021). However, the actual regolith thickness is poorly constrained or unknown in many cases.</p> <p>In this study, the uncertainty introduced into seismic shaking models from the assumed active layer thickness is investigated by comparing the relative timescales of crater relaxation (crater erasure). We use the Richardson et al., (2004) seismic shaking model, as modified by Michel et al., (2009) for Itokawa with impactor populations from O’Brien and Greenberg (2005). Our results show that decreasing the active layer depth leads to a nonlinear increase in the time to erase a crater. The total increase in time to erasure for a crater 20 m in diameter when changing from regolith depths of 5 m to 0.1 m is over three magnitudes, mostly accommodated between depths of 1 m to 0.1 m. We also investigated the relative timescales of crater erasure for craters of different sizes. Increasing the crater diameter leads to a non-linear increase in crater erasure time, with a 10<sup>3</sup> increase in erasure time when the diameter is increased from 5 m to 100 m.</p> <p>The high sensitivity of crater erasure time on active layer depth and crater size implies that care should be taken when inferring surface properties, in particular asteroid surface age, time since a resetting event, or depth/diameter comparisons between asteroids with different crater populations.</p> <p> </p> <p>References</p> <p>                  Daly, R.T., Bierhaus, E.B., Barnouin, O.S., Daly, M.G., Seabrook, J.A., Roberts, J.H., Ernst, C.M., Perry, M.E., Nair, H., Espiritu, R.C., Palmer, E.E., Gaskell, R.W., Weirich, J.R., Susorney, H.C.M., Johnson, C.L., Walsh, K.J., Nolan, M.C., Jawin, E.R., Michel, P., Trang, D., Lauretta, D.S., 2020. The Morphometry of Impact Craters on Bennu. Geophys. Res. Lett. 47, e89672. doi:10.1029/2020GL089672</p> <p>Michel, P., O'Brien, D.P., Abe, S., Hirata, N., 2009. Itokawa's cratering record as observed by Hayabusa: Implications for its age and collisional history. Icarus 200, 503–513. doi:10.1016/j.icarus.2008.04.002</p> <p>Noguchi, R., Hirata, N., Hirata, N., Shimaki, Y., Nishikawa, N., Tanaka, S., Sugiyama, T., Morota, T., Sugita, S., Cho, Y., Honda, R., Kameda, S., Tatsumi, E., Yoshioka, K., Sawada, H., Yokota, Y., Sakatani, N., Hayakawa, M., Matsuoka, M., Yamada, M., Kouyama, T., Suzuki, H., Honda, C., Ogawa, K., Kanamaru, M., Watanabe, S.-I., 2021. Crater depth-to-diameter ratios on asteroid 162173 Ryugu. Icarus 354, 114016. doi:10.1016/j.icarus.2020.114016</p> <p>O'Brien, D.P., Greenberg, R., 2005. The collisional and dynamical evolution of the main-belt and NEA size distribution, Icarus 178, 179</p> <p>Richardson, J.E., Melosh, H.J., Greenberg, R., 2004. Impact-induced seismic activity on asteroid 433 Eros: a surface modification process. Science 306, 1526–1529. doi:10.1126/science.1104731</p> <p>Richardson, J.E., Melosh, H.J., Greenberg, R.J., O'Brien, D.P., 2005. The global effects of impact-induced seismic activity on fractured asteroid surface morphology. Icarus 179, 325–349. doi:10.1016/j.icarus.2005.07.005</p> <p>Richardson, J.E., Steckloff, J.K., Minton, D.A., 2020. Impact-produced seismic shaking and regolith growth on asteroids 433 Eros, 2867 Šteins, and 25143 Itokawa. Icarus 347, 113811. doi:10.1016/j.icarus.2020.113811</p>

Shale, Quakes, and High Stakes: Regulating Fracking-Induced Seismicity in Oklahoma, USA and Lancashire, UK

High-volume hydraulic fracturing combined with horizontal drilling has “revolutionized” the United States’ oil and gas industry by allowing extraction of previously inaccessible oil and gas trapped in shale rock [1]. Although the United States has extracted shale gas in different states for several decades, the United Kingdom is in the early stages of developing its domestic shale gas resources, in the hopes of replicating the United States’ commercial success with the technologies [2, 3]. However, the extraction of shale gas using hydraulic fracturing and horizontal drilling poses potential risks to the environment and natural resources, human health, and communities and local livelihoods. Risks include contamination of water resources, air pollution, and induced seismic activity near shale gas operation sites. This paper examines the regulation of potential induced seismic activity in Oklahoma, USA, and Lancashire, UK, and concludes with recommendations for strengthening these protections.

Modelling the Dynamic Relationship Between Mining Induced Seismic Activity and Production Rates, Depth and Size: A Mine-Wide Hierarchical Model

The dynamic properties of mining induced seismic activity with respect to production rate, depth and size are studied in seven orebodies in the same underground iron ore mine. The objective is to understand the relationship between the measured seismic activity and the: seismic decay time, planned production rate, production size and mining depth. This relationship is the first step to individually customise the production rate for each orebody in the mine, make short-term predictions of future seismicity given planned productions, and to find out in what way the available predictors affect the seismicity. The seismic response with respect to the dependent variables is parametrised and the estimated decay times for each orebody, which are of particular interest here, are compared. An autoregressive model is proposed to capture the dynamic relationship between the induced seismic activity, the current production rate and the past seismic activity. Bayesian estimation of the parameters is considered and parameter constraints are incorporated in the prior distributions. The models for all orebodies are tied together and modelled hierarchically to capture the underlying joint structure of the problem, where the mine-wide parameters are learnt together with the individual orebody parameters from the observed data. Comparisons between the parameters from the hierarchical model and independent models are given. Group-level regressions reveal dependencies on size and mining depth. Model validation with posterior predictive checking using several discrepancy measures could not detect any model deficiencies or flaws. Posterior predictive intervals are evaluated and inference of model parameters are presented.

The LArge‐n Seismic Survey in Oklahoma (LASSO) Experiment

ABSTRACT In 2016, the U.S. Geological Survey deployed >1800 vertical-component nodal seismometers in Grant County, Oklahoma, to study induced seismic activity associated with production of the Mississippi limestone play. The LArge‐n Seismic Survey in Oklahoma (LASSO) array operated for approximately one month, covering a 25 km by 32 km region with a nominal station spacing of ∼400 m. Primary goals of the deployment were to detect microseismic events not captured by the sparser regional network stations and to provide nearly unaliased records of the seismic wavefield. A more complete record of earthquakes allows us to map the spatiotemporal evolution of induced event sequences and illuminates the structures on which the events occur. Dense records of the seismic wavefield also provide improved measurements of the earthquake source, including focal mechanisms and stress drops. Taken together, we can use these findings to glean insights into the processes that induce earthquakes. Here, we describe the array layout, features of the nodal sensors, data recording configurations, and the field deployment. We also provide examples of earthquake waveforms recorded by the array to illustrate data quality and initial observations. LASSO array data provide a significant resource for understanding the occurrence of earthquakes induced by wastewater disposal.

Estimation of Tropospheric and Ionospheric Delay in DInSAR Calculations: Case Study of Areas Showing (Natural and Induced) Seismic Activity

The article presents a proposal to make simultaneous allowance for both ionospheric and tropospheric corrections in differential synthetic aperture radar interferometry (DInSAR) measurements. Atmospheric delay in the interferometric phase may cause the detection of terrain-surface changes to be impossible or significantly distorted. This fact remains of special importance in the case of surface changes that show limited amplitude and spatial range. Two areas were chosen to verify the validity of the proposed solution. The first area includes terrains affected by underground copper-ore mining activity (Poland), which shows high induced seismic activity. Mining tremors recorded in this area cause the terrain surface to locally subside. The authors analyzed three tremors that were recorded in 2016, 2017, and 2019. Each of the tremors exceeded a magnitude of Mw 4.0. The second area is located in the coastal region of Chile, in the Cardenal Caro province. In this case, the authors focused on a series of three earthquakes recorded on 11 March 2010. The strongest of the earthquakes was of Mw 7.0 magnitude. In the first case, calculations were based on obtained data from the Sentinel 1 satellites, and in the second case from the ALOS-1 satellite. It is demonstrated that simultaneous allowance for both the tropospheric and ionospheric corrections significantly improves the final results. The authors were also able to use the analyzed cases to demonstrate that implementation of the corrections does not have negative influence on the range and magnitude of local ground-surface deformations. At the same time, such implementation minimizes local displacement fluctuations and reduces displacement values in areas affected by deformations. The examples used in the article served to show that tropospheric correction is mainly responsible for global corrections (i.e., within the whole analyzed spatial range), while ionospheric correction reduces local fluctuations.