A comparison of seismic risk maps for Italy

National seismic risk maps are an important risk mitigation tool as they can be used for the prioritization of regions within a country where retrofitting of the building stock or other risk mitigation measures should take place. The production of a seismic risk map involves the convolution of seismic hazard data, vulnerability predictions for the building stock and exposure data. The seismic risk maps produced in Italy over the past 10 years are compared in this paper with recent proposals for seismic risk maps based on state-of-the-art seismic hazard data and mechanics-based vulnerability assessment procedures. The aim of the paper is to open the discussion for the way in which future seismic risk maps could be produced, making use of the most up-to-date information in the fields of seismic hazard evaluation and vulnerability assessment.     

Clast fabric and mass wasting on Asteroid 25143-Itokawa: Correlation with talus and other periglacial features on Earth

Regolith on Itokawa, a 300-meter diameter near-Earth asteroid, first imaged by the Hayabusa Spacecraft in 2005, provides a new database of information on surface features and different space-form (i.e. landform) assemblages. The satellite imagery was taken from distances of near-surface and 2 km to 63 m, the latter giving image resolutions of 6 mm/pixel. Small regolith-covered asteroids produce rubble-covered surface mantles, resident on slopes ranging from 27° relative to an artificial horizon, and distributed non-uniformly across the surface. Low gravity acceleration on Itokawa means that clast movement is largely the result of global vibrations caused by impacts producing seismic shaking. Gravel-network orientations, previously correlated with imbricated stream gravels on Earth by the Hayabusa Scientific Team (Miyamoto, H., Yano, H., Scheeres, D.J., Abe, S., Barnaouin-Jha, O., Cheng, A.F., Demura, H., Gaskell, R.W., Hirata, N., Ishiguro, M., Michikami, T., Nakamura, A.M., Hakamura, R., Saito, J., Sasaki, S., 2007. Regolith migration and sorting on asteroid Itokawa. Science. 316, 1011–1014, Fig. 2F), are here partly correlated with talus and stone-banked lobe accumulations on Earth. We present ‘sliderock’ accumulations on Itokawa correlated with talus accumulations on Earth from several high, middle and low latitude Cryic localities. The presence of debris-flow accumulated clastic material indicates the presence of permafrost and issuance of meltwater at some time in the past, presumably linked to an orbital or solar radiation perturbation. The available data indicate the presence of water, at least on a punctuated time scale; along with the presence of Fe, the combination of the two suggesting weathering processes and a dynamic surface geology on what was previously considered to be a dry, barren, lifeless world.     

Subduction,fluids, and accessory minerals: a celebration of the career of Sorena S. Sorensen

ABSTRACT

This is a preface to the topical issue entitled ‘Subduction, Fluids, and Accessory Minerals: A Celebration of the Career of Sorena S. Sorensen’     

Carbon Isotope Analysis to Evaluate Nanoscale Fe(O) Treatment at a Chlorohydrocarbon Contaminated Site

Remediation of groundwater contaminated by chlorinated hydrocarbons via in situ technologies such as direct injection of nanoscale zero valent iron (ZVI, Fe(O)) particles is increasingly common. However, assessing target compound degradation by abiotic processes is difficult because (1) the injection may displace the contaminant plume so that concentration measurements alone are often inconclusive and (2) biodegradation may also occur, making it challenging to identify and evaluate the abiotic degradation component. In this study, trichloroethylene (TCE) and 1,1,1-trichloroethane (1,1,1-TCA) were treated in a highly heterogeneous hydrogeologic setting. The purpose of this study was to evaluate the potential for compound-specific stable isotope analysis (CSIA) to monitor the effectiveness of ZVI injection by assessing TCE and 1,1,1-TCA degradation. Prior to ZVI injection, carbon isotope measurements demonstrated biodegradation of TCE by native microorganisms. This in situ biodegradation was quantified by measuring the enrichment of ¹³C in TCE samples downstream of the suspected source. When ZVI was injected through only two injection wells, no changes in TCE and 1,1,1-TCA isotope signatures were detected compared to preinjection values. In contrast, when ZVI was injected through 11 wells covering a greater portion of the contaminated area, 5 out of 10 monitoring wells showed further enrichment of ¹³C in either TCE or 1,1,1-TCA, indicating additional target compound transformation. The abiotic nature of this TCE transformation was confirmed through temporal trends in carbon isotope values of the putative transformation products cis-dichloroethylene (cis-DCE), ethene and ethane. This demonstrates the usefulness of CSIA in distinguishing abiotic vs. biotic transformation in the field.     

Determination of focal depth by two waveformbased methods: A case study for the 2008Panzhihua earthquake

With the 2008 M_S6.1 Panzhihua earthquake as a case study, we demonstrate that the focal depth of the main shock can be well constrained with two approaches: (1) using the depth phase sPL and (2) using full waveform inversion of local and teleseismic data. We also show that focal depths can be well constrained using the depth phase sPL with single broadband seismic station. Our study indicates that the main shock is located at a depth of 11 km, much shallower than those from other studies, confirming that the earthquake occurs in upper crust. Aftershocks are located in the depth range of 11-16 km, which is consistent with a ruptured near vertical fault whose width is about 10 km, as expected for an M_S6.1 earthquake.