张其昀的地理思想和学术成就

张其昀(1901—1985)是我国近代地理学的创建者之一。他在地理教育以及人文地理学的广泛领域卓有建树。本文阐述他的学术成就,并探讨他的地理思想。     

利用旱涝县次建立历史时期旱涝指数序列的试验*

本文利用27万条自然灾害史料记载,整理出我国东部及南部85个地区的受灾县次记录,分析了这些记录的可靠性,建立了这些地区1471—1950年的旱涝指数序列,并以北京地区为例,详细说明了利用旱涝县次建立旱涝指数序列的过程,分析了这种方法的可靠性。     

Regional variation of Rayleigh wave attenuation coefficients in the Eastern Pacific

Seismograms recorded for five earthquakes on the east Pacific rise have been analyzed to obtain the attenuation coefficients of the fundamental Rayleigh mode for the eastern Pacific in the 15–110 second period range. The attenuation coefficients have been obtained using two new methods, a reference-station method, and an iterative method by which the seismic moment and regionalized attenuation coefficient values are obtained simultaneously after considering the effect of the source directivity and time-function. The reference-station method was applied to the entire eastern Pacific, excluding paths along the east Pacific rise. When using the iterative method we divided the eastern Pacific into three sub-regions, designated as the north-eastern Pacific, the Nazca plate and the east Pacific rise. Although much scatter is present, the data suggest that attenuation coefficients for the Nazca plate are higher than those for the northeastern Pacific, and both are substantially higher than average values obtained for the entire Pacific Ocean. Two paths that lie along or near the east Pacific rise are characterized by especially high attenuation coefficients. These values suggest that a low-Q zone exists beneath that narrow feature.     

La sismicité en corse: Revue historique et etude macrosismique de quelques evénéments récents

Résumé L'étude des documents (archives, presse et catalogues sismiques) que nous avons consultés, nous a permis de remonter jusqu'à la fin du XVIIIe siècle dans l'histoire sismologique corse. Le nombre des séismes ressentis (épicentres en mer ou sur l'île) recensés pendant ces deux siècles et demi est relativement faible. Les intensités maximales ont parfois atteint le degré VI, plus rarement VII. L'activité sismique touche principalement une région située au Nord-Est de la Corse, au voisinage de failles au rejeu récènt et séparent le domaine de la Corse schisteuse (alpin) du domaine de la Plaine Orientale (Quaternaire, Néogène). Une crise sismique récente (1978–1979) a de nouveau secoué cette même région où on a suggéré l'activité actuelle de certaines de ces failles. Les plus importants de ces séismes (I _max=VI et V) ontifait l'objet d'enquêtes macrosismiques qui permettent d'en préciser les épicentres. Deux d'entre-eux ont été étudiés en détail (3 avril 1978 et 27 mars 1979); en utilisant la relation de Kövesligethy, les hypocentres se situent respectivement à 4,5±0.5 km et vers 5 km, pour des coefficients d'absorption de 0,020 et 0,031. Ces profondeurs indiquent que ces deux séismes ont mis en jeu des éléments superficiels de la croûte corse (30 km).

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The documents that we have compiled (archives, newspaper reports and seismic catalogues) enabled us to go back to the end of the 18th century in the seismic history of Corsica. The number of felt earthquakes (epicentres off shore or on the island) which were documented during the two and a half centuries is relatively low. Maximum intensities have reached VI or rarely VII. The seismic activity is mainly located in the North-East of Corsica, near faults which have recently been active between the Corse schisteuse (Alpine domain) and the Plaine Orientale (Quaternary, Neogene). A seismic crisis happened recently (1978–1979) in this area where present activity of some of these faults has been suggested. Macroseismic studies have been conducted for the main shocks (I _max=VI and V) in order to locate them accurately. Two among them (April 3, 1978 and March 27, 1979) are studied here in detail. Using the Kövesligethy formula hypocenters are respectively found at 4.5±0.5 km and around 5 km, whereas the corresponding absorption factors are 0.020 and 0.031. Such depths show that the two events affected the upper crust of Corsica (30 km).

Contribution n^o 321 de l'Institut de Géophysique, Ecole Polytechnique Fédérale de Zürich.     

Entropy inference of recurrence models for variability analysis of extreme events

A complete methodology is developed to analyze the recurrence of extreme environmental events and its variability as time without further events elapses. Firstly we investigate the conditioned recurrence inference problem consisting in the selection of a probability model for the interarrival time between extreme events, given a contexto-factual evidence conditioned by the time elapsed since the last of such events. Two ways to include this condition can be considered, which yield alternative conditioned evidences and convert the former problem into two distinct ones, thus giving rise to a possible consistency violation. These problems are formalized within the logical probability framework, in a plausible logic language that allows a suitable expression of the available observational data. They are solved using the REF relative entropy method with fractile constraints, and their solutions are compared at all inference levels. It is concluded that the two conditioning ways are not really mutually exclusive and that a unique global solution to the conditioned inference can be obtained using this procedure. An example illustrates an application of the methodology to the variability analysis of the recurrence time between historical inundations of the Guadalquivir river in Spain, as time elapses with no new floods.Acknowledgments. Support for this work was provided by DGI of Spain as the grant REN2000-2988-E/CLI and the research project REN2002-01337/CLI.