The great historical 1755 earthquake. Effects and damage in Spain

The access to the complete reports sent in answer of a Royal enquire relative to the 1755 earthquake (Archivo Historico Nacional, 1756) provided us with information more comprehensive than that included in the analysis of such documents prepared by the Spanish Royal Academy of History in 1756 (Real Academia de la Historia, 1756). With such data, we have made a new study of the shock centred mainly in the following points: number of victims, source parameters (including moment magnitude and epicentral location),intensity map and seismogeological effects compared with those expected from the EMS-98. Relevant results from this analysis are: a new intensity attenuation law for earthquakes from the region of the 1755 shocks and first approximation damage probability matrices for buildings of the types common in the XVII to XIX centuries affected by large, distant earthquakes.     

Theoretical seismograms for block structures

Summary In constructing theoretical seismograms for large models with block structures, approximate methods are particularly efficient. For example, in treating Earth's crust block models, the ray method with various modifications for including diffracted waves can be used. Smaller block structures, of dimensions comparable to a wavelength, are efficiently treated by direct numerical methods. In this way practically important problems of engineering seismology, seismic microzoning, etc., can be solved. The method of so-called conservative diference schemes combines effectively the advantageous features of both the standard finite element and finite difference methods. The basic properties of the method, as well as some features of the corresponding Fortran IV program LATER, are explained on a computational example. The example concerns a highly simplified evaluation of the seismic response of the earth fill. In the frequency range under study two resonance frequencies are identified. Moving along the surface of the fill, from the base to the peak, the predominant frequency decreases. Some prospects of direct numerical methods in seismology are briefly discussed in concluding section.Presented at the Workshop on Seismic waves in laterally inhomogeneous media, Liblice (Czechoslovakia), 27. 2–3. 3. 1978.     

Two-dimensional correlation of geophysical data applied to the heat flow and earth's crust thickness patterns in Czechoslovakia

Summary A simple method for the mutual correlation of various geophysical fields is proposed to disclose their prospective inherent correlations. Some problems connected with the statistical and physical confidence of the resulting maps of the correlation coefficient are mentioned. The correlation between the surface heat flow pattern and the crustal thickness on the territory of Czechoslovakia is presented as an example and briefly discussed in terms of crustal structure.     

Accuracy of deflections of vertical determined from discrete solution of the geodetic boundary value problem

Summary The general problem of determining the figure of the earth leads to the solution of the geodetic boundary value problem. By its discrete approximation we obtain the discrete disturbing potential that maintains all properties of the original problem. Thus, the discrete approximation of the disturbing potential can be used in studying the behaviour of the earth's gravity field outside the disturbing masses. The deflections of the vertical are one of the quantities describing the behaviour of the earth's gravity field. A method for their computation from the discrete solution of the geodetic boundary value problem is put forth and estimates for its accuracy are given.     

Rheological modelling of measuring systems of quartz gravity meters

Summary Some phenomena, recorded during pressure tests of quartz gravity meters, are studied theoretically using a model of the visco-elastic continuum. Expressions, describing the response of the measuring system as a function of the time variation of pressure disturbances, are derived by solving the appropriate rheological equations.

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A water balance model to estimate climate change impact on groundwater recharge in Yucatan Peninsula,Mexico

ABSTRACT

The aim of this paper is to estimate the effect that climate change will have on groundwater recharge at the Yucatan Peninsula, Mexico. The groundwater recharge is calculated from a monthly water balance model considering eight methods of potential and actual evapotranspiration. Historical data from 1961–2000 and climate model outputs from five downscaled general circulation models in the near horizon (2015–2039), with representative concentration pathway (RCP) 4.5 and 8.5 are used. The results estimate a recharge of 118 ± 33 mm·year^–1 (around 10% of precipitation) in the historical period. Considering the uncertainty from GCMs under different RCP and evapotranspiration scenarios, our monthly water balance model estimates a groundwater recharge of 92 ± 40 mm·year^–1 (RCP4.5) and 94 ± 38 mm·year^–1 (RCP8.5) which represent a reduction of 23% and 20%, respectively, a result that threatens the socio-ecological balance of the region.