Project catalogue and seismic hazard maps : Final report. Seismic hazard in Latin America and the Caribbean

Las agencias (UNAM por México, CERESIS por América del Sur, CEPREDENAC por América Central y UWI por el Caribe) de cada una de las cuatro regiones que comprende el proyecto (además del IPGH) integraron catálogos revisados de sismicidad histórica y registrada instrumentalmente. Cada uno de ellos fue incorporado en un catálogo de proyecto, siguiendo los lineamientos establecidos por el Comité Directivo, con la ayuda de programas escritos especialmente para este propósito por la Comisión de Geofísica del IPGH.(AU)

A revised earthquake catalogue for the Eastern Caribbean Region : 1513-1992

We presente a revised earthquake catalogue for the eastern Caribbean region 8 N to 22.5 N, 58 W to 70 W covering the period 1530 to 1993. Sizes of all events for which sufficient information exists have been expressed in terms of seismic moment either measured directly or derived from earthquake magnitude by theoretical and empirical formulae. From 1530 to 1900 the sources of information consist entirely of written accounts of felt earthquakes. The completeness of this part of the catalogue varies throughout the region but it is probably complete down tro magnitude (M06.5 to 7 since 1800 and perhaps as far back as 1600 for some parts of the region. From 1900 onwards an increasing number of instrumentally-determined epicentres and magnitudes are available but reports of felt earthquakes continued to exceed instrumental observations at least until 1950. During this period the lower magnitude for completeness is in the range of 5.5 to 6. After 1950 the establishment of more modern seismograph stations within the region gradually improved the location threshold but the major improvement did not occur until 1964 when the almost simultaneous completion of the WWSSN and the establishment of the ISC further reduced the threshold to about 4.0. Within limited regions such as the central Lesser Antilles and the Trinidad-Tobago region where local seismograph systems are particualrly efficient the location threshold is now down to the microearthquake level.(AU)

Revised estimates of the levels of ground acceleration and velocity with 10 / probability of exceedance in any 50-year period for the Trinidad and Tobago region

We presente estimates of the levels of ground acceleration and velocity with 90

probability of non-exceedeance in any 50-year period for the Trinidad and Tobago region. The estimates have been made using a revised catalogue of eastern Caribbean earthquakes as the data base. In comparison with previous estimates, the levels of ground acceleration are in the same general range (200-400 gals) but the variation within the islands has changed. The level in the northwestern part of Trinidad, including Port of Spain, is about 250 gals. In the southeastern part of Trinidad the level has increased to 350-450 gals. This increase is because of the recognition of an active seismogenic source to the southeast of Trinidad which was unknown at the time of the previous studies. The level in Tobagp is increased to 250 gals, again because of the identification os a shallow seismogenic source in the southwestern part of the island. Ground velocity levels are more uniform and do not vary significantly from 20cm/sec in any part of the islands. There are no previous estimates with which to make comparisons.(AU)

Explosive submarine eruptions of kick-'Em-Jenny volcano : Preliminary investigations of the potential tsunami hazard in the Eastern Caribbean region

Kick-'em-Jenny is a submarine volcano situated to the north of Grenada in the Lesser Antilles. A preliminary study suggests that the volcano is a prime candidate for tsunamigenic eruptions on a potentially hazardous scale, possibly affecting the whole of the Eastern Caribbean region. The uniqueness of individual volcanic eruptions means that attempts to generalize tsunamigenic mechanisms are extremely tentative. However, the theory of underwater explosion generated water waves (Le Mehaute, 1971) is applicable to submarine volcanoes to model explosive eruptions. Using this theory, initial maximun ocean surface displacements are calculated for Kick-'em-Jenny hydroeruptions, corresponding to various event magnitudes (up to a 'worst-case' scenario eruption on the scale of Krakatau, 1883). Wave propagation theories are then applied to the resulting tsunami wave dispersion, before beach shoaling equations are used to estimate the maximum tsunami run-up at adjacent coastal areas. Maps of the region have been prepared showing the travel times and maximum run-up amplitudes of the waves along coastlines. Finally, an attempt is made to assess how great a hazard the volcano represents, by considering the probability of each magnitude event occurring.(AU)

Current status of seismicity studies in the Greater and Lesser Antilles

The present status of seismicity studies in the Greater and Lesser Antilles is discussed with reference to the adequacy of the existing data base for studies of Caribbean tectonics, of earthquake hazard and of the recognition of seismicity petterns important for seismic hazard studies and earthquake prediction. It is demonstrated that existing data bases such as those of the NEIC and ISC are generally inadequate for these purposes. Two reasons for this are identified. One reason is that in some crucial areas of the Caribbean, notably the western two-thirds of the island of Hispaniola and Jamaica, an insufficient number of seismograph stations is in operation. A second reason is that there is insufficient data exchange between the existing agencies within the region and that there is insufficient data exchange between the existing agencies within the region and that many valuable original data are either unavailable or are published only in obscure reports. It is suggested that rectification of these two defects should be a major objective of the forthcoming International Decade of Natural Hazard Reduction. In the meantime, researches who use existing seismicity catalogues should pay close attention to their completeness and homogeneity.(AU)

Contemporary seismicity of the Trinidad and Tobago region : Tectonic and earthquake hazard implications

Results are presented fron the first eleven years of operation of a radio-linked seismograph network in the Trinidad and Tobago region. All earthquakes of magnitude (mb) greater than about 2.8 have been relocated using the method of joint hypocentral determination (JHD). The results show an extremely complex pattern of seismicity and are presented as a set of maps showing earthquakes in different depth ranges. Important features of the earthquake distribution are that the supposed sontinuation of the El Pilar fault through the northern part of Trinidad has not been seismically active for at least the past decade and that there is a significant source of immediate-depth earthquakes to the east of Trinidad, the existence of which was previously unknowm. Our interpretation of the results favours oblique ongoing collision between the Lesser Antilles island arc and the South American continent rather than predominantly east-west strike slip motion.(AU)