Reply to “Comment on ‘Influence of Focal Mechanism in Probabilistic Seismic Hazard Analysis’ by Vincenzo Convertito and André Herrero,” by F. O. Strasser, V. Montaldo, J. Douglas, and J. J. Bommer

We thank F. O. Strasser, V. Montaldo, J. Douglas, and J. J. Bommer for the interest they have shown in our article (Convertito and Herrero, 2004). Strasser et al. (2006) present a critical comment of our work arguing that the solution proposed by Bommer et al. (2003) is a better solution. Note that the authors are nearly the same in both article and comment, except for V. Montaldo. Because this brief article is a reply, we will focus on the arguments directly concerning our article. The main objection supported by Strasser et al. (2006) is that the method we proposed is not appropriate to "styleof-faulting" correction. We completely agree with this assertion because it is simply not the scope of our article. We speak about "focal mechanism" intended as radiation pattern and nothing else. This point is clearly stated in the introduction of Convertito and Herrero (2004): "in this article we consider that the focal mechanism influence is only expressed by radiation pattern changes. In particular we do not consider any tectonic influence, stress drop variation or dynamic effects." The style-of-faulting parameter, even if its identity is blurred (e.g., Bommer et al., 2003), is an empirical definition of a complex set of physical conditions including the tectonic regime, the medium behavior, rock mechanics, rupture dynamics, and so on. In our opinion, the style of faulting is simply too complex to be used directly in our approach. Because the scope of our article is to show how it is possible to insert inside the main equation of probabilistic seismic-hazard analysis (PSHA; e.g., Cornell, 1968), simple physical parameters of the seismic source, that is, how it is possible to integrate deterministic parameters inside a probabilistic approach, we have chosen a small target, limiting ourselves only to the radiation pattern. We believe that the same approach can be used to insert many other parameters of the seismic source inside PSHA by using only a theoretical approach such as the fault strike (which has already been shown by Convertito, 2004), the directivity and stress drop. The second important argumentation is that a method based on regression (i.e., Bommer et al., 2003) is better than the method we propose. Once again we agree with Strasser et al. (2006) and this is clearly stated in the conclusion of our article: "when an attenuation law, including a faulting style parameter, is available for a given region, the use of this attenuation law gives a more reliable estimate of the hazard than the one obtained using the corrective coefficient we propose in this article.

Development of a site conditions map for the Campania-Lucania region (southern Apennines, Italy)

Having a reliable site conditions estimate is an important step to analyze and predict earthquake ground motions. To provide this information for the Campania-Lucania region (southern Apennines, Italy), in the framework of a collaboration with regional civil protection agency, geologic units shown on 1:250,000 scale geologic map, have been sorted together into four categories based on age and geological similarities. According to the site classification defined in engineering building codes, we have assigned to each site classes, a value or range of values of the average shear-wave velocity to 30 m (Vs30) and of the site dominant period. Thus, we have digitized the category boundaries from the map tracing only the geologic contacts that separate units of different site classes. The accuracy of the site-conditions map is only limited by the number of Vs profiles, used to compute the Vs30, and geologic data available so far. Analyses with new data will allow updates and modifications of this map. Anyhow, the resulting site classification map may be an helpful tool to better characterizing the sites effects for those applications where amplification values at large scale are need, such as ground-shaking maps or seismic hazard maps

Italian Map of Design Earthquakes from Multimodal Disaggregation Distributions: Preliminary Results.

Probabilistic seismic hazard analysis allows to calculate the mean annual rate of exceedance of ground motion intensity measures given the seismic sources the site of interest is subjected to. This piece of information may be used to define the design seismic action on structures. Moreover, through disaggregation of seismic hazard, it is possible to identify the earthquake giving the largest contribution to the hazard related to a specific IM value. Such an information may also be of useful to engineers in better defining the seismic treat for the structure of interest (e.g., in record selection for nonlinear seismic structural analysis). On the other hand, disaggregation results change with the spectral ordinate and return period, and more than a single event may dominate the hazard, especially if multiple sources affect the hazard at the site. In this work disaggregation for structural periods equal to 0 sec and 1.0 sec is presented for Italy, with reference to the hazard with a 475 year return period. It will be discussed how for the most of Italian sites more than a design earthquake exist, because of the modelling of seismic sources

The Health of British Seamen in the West Indies, 1770 - 1806

This thesis examines the impact of disease and mortality on the Royal Navy in the West Indies from 1770 to 1806. It also investigates the navy’s medical branch which was established to manage the care of sick seamen. Using an interdisciplinary approach, this thesis produces a cohesive understanding of how disease and mortality affected the navy’s presence in the West Indies and the ways in which the navy attempted to mitigate their impact. This thesis explores various aspects of naval medicine including the history of the Sick and Hurt Board, the diseases which distressed seamen, the medicines distributed by the navy, the key personnel who were integral in generating changes to the medical system and the development of hospital facilities. Largely based on Admiralty records including correspondence and minutes from the Sick and Hurt Board, ships’ muster books and surgeons’ journals, this thesis investigates the most prevalent diseases in the West Indies and the prescribed treatments advocated by the navy. It then examines how these diseases and treatments affected seamen on board ships in that region through a quantitative analysis; then focuses on a number of the integral naval personnel who ushered in sweeping changes to naval medicine; and explores the navy’s increasing desire to transition from hired sick quarters to purpose-built naval hospitals on various West Indies islands. It concludes with a case study of the development of Antigua naval hospital which demonstrates the effectiveness of these facilities in convalescing sick seamen. Through a quantitative analysis of ships’ muster books, this thesis argues that the levels of sickness and mortality in the navy in the West Indies during the late eighteenth century are largely exaggerated in historical studies while also discrediting the myth that those islands were the ‘white man’s graveyard’ for many naval personnel. By surveying over 100,000 seamen on board ships in that region, sickness and mortality figures emerge which indicate that, on average, less than 4 per cent of seamen were on the sick list at any given time and only a small percentage died, meaning that the majority remained on active duty. This thesis then argues that many of the changes to the navy’s medical system that facilitated such low percentages were primarily instigated by surgeons, physicians and captains who identified beneficial medicines and championed their general distribution among the entire fleet. By looking at these aspects of naval medicine through a multidisciplinary lens rather than a purely administrative one, it is possible to understand the true state of health of British seamen in the West Indies during the last quarter of the eighteenth century

Seismic hazard disaggregation in the Molise region, Italy: the case study of Campobasso

Large scale experimentations play a relevant role in the earthquake engineering research, similarly Structural Health Monitoring is able to give information of real structures. A few geotechnical structures are documented, because only data on seismic permanent deformations are available. The present paper deals with seismic hazard of the site of the Student House at University of Molise, where a geotechnical monitoring system has been designed and is currently under implementation. It is aimed at refining the seismic hazard characterization for identifying a set of relevant earthquakes for the theoretical analysis of the structure. Reference earthquakes expressed in terms of magnitude (M), distance (R) and ε, were therefore investigated. Uniform hazard spectra at different structural periods for a 475-year return period were disaggregated. Shapes of both the joint and marginal probability density functions were studied and the first two modes of M, R and ε were extracted and discussed

An Automated Method for Mapping Independent Spatial b Values

We present an automated method for mapping the b values. The algorithm is very simple and presents three advantages: (a) it does not requires any tuning of the parameters like, for instance, a fixed cell size or a maximum radius of the cell; (b) it implies a more appropriate use of the catalog, by using almost all the events in the catalog used (with a tolerance of 1%) with no overlap; (c) it implies the full independence of the b values, thus allowing the statistical comparison of the results using standard tests. Although the resulting b values are comparable with those obtained by applying the other methods of common use in seismology, these latter (a) leave out many earthquakes from the analysis, with loose of useful information, (b) produce diffuse cells overlapping aiming at reaching many cells of the grid in order to get the correct number of events in each cell, and (c) results in correlated b values, which do not allow the test of significance for the differences in the b values. Finally, due to the independence from any ad hoc a-priori choice, our method is suitable for automatic and operator-free procedures.Plain Language Summary The methods usually used in seismology for mapping the b value require the tuning of some parameters depending on the analyzed catalog. Here we propose a method that only implies the choice of the minimum number of earthquakes needed to obtain reliable b value estimates, which does not depend on the specific cases. Due to the mutual complete independence of the resulting b values, the proposed method allows the use of standard statistical tests to compare the results

Using ground motion prediction equations to monitor variations in quality factor due to induced seismicity: a feasibility study

Sub-surface operations for energy production such as gas storage, fluid reinjection or hydraulic fracking may modify the physical properties of the rocks, in particular the seismic velocity and the anelastic attenuation. The aim of the present study is to investigate, through a synthetic test, the possibility of using empirical ground-motion prediction equations (GMPEs) to observe the variations in the reservoir. In the synthetic test, we reproduce the expected seismic activity (in terms of rate, focal mechanisms, stress drop and the b value of the Gutenberg-Richter) and the variation of medium properties in terms of the quality factor Q induced by a fluid injection experiment. In practice, peak-ground velocity data of the simulated earthquakes during the field operations are used to update the coefficients of a reference GMPE in order to test whether the coefficients are able to capture the medium properties variation. The results of the test show that the coefficients of the GMPE vary during the simulated field operations revealing their sensitivity to the variation of the anelastic attenuation. The proposed approach is suggested as a promising tool that, if confirmed by real data analysis, could be used for monitoring and interpreting induced seismicity in addition to more conventional techniques

Subduction age and stress state control on seismicity in the NW Pacific subducting plate

Intermediate depth (70-300 km) and deep (> 300 km) earthquakes have always been puzzling Earth scientists: their occurrence is a paradox, since the ductile behavior of rocks and the high confining pressure with increasing depths would theoretically preclude brittle failure and frictional sliding. The mechanisms proposed to explain deep earthquakes, mainly depending on the subducting plate age and stress state, are generally expressed by single parameters, unsuitable to comprehensively account for differences among distinct subduction zones or within the same slab. We analyze the Kurile and Izu-Bonin intraslab seismicity and detail the Gutenberg-Richter b-value along the subducted planes, interpreting its variation in terms of stress state, analogously to what usually done for shallow earthquakes. We demonstrate that, despite the slabs different properties (e.g., lithospheric age, stress state, dehydration rate), in both cases deep earthquakes are restricted to depths characterized by equal age from subduction initiation and are driven by stress regimes affected by the persistence of the metastable olivine wedge