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Spatial variations of b-value in the subduction zone of Central America
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
2003 (English)In: Geofísica Internacional, ISSN 0016-7169, Vol. 42, no 4, 575-587 p.Article in journal (Refereed) Published
Abstract [en]

requency-magnitude distribution along the Mid-American Trench (MAT) has been studied by means of 2345 earthquakesduring the period 1964-1994. We used the regional MIDAS catalogue with a magnitude of completeness of 4.2. To resolve the bvalueas a function of depth (one dimensional approach), we applied vertically sliding windows containing a constant number ofevents. To obtain more details in the b distribution, we projected catalogue hypocenters in three selected regions (approximatelyGuatemala and El Salvador, Nicaragua, Costa Rica), onto planes perpendicular to the trench. The b-values were calculated insliding cylindrical volumes (two-dimensional approach) containing a constant number of earthquakes and centered at nodes of a5 km x 5 km grid. The b-value varies significantly along a large part of MAT. High b-values were identified in the upper part of theslab at depths of 80-110 km beneath Guatemala-El Salvador and at depths 130-170 km beneath Nicaragua. Anomalous (high) bvaluesin the lower part of the slab were located at depths of 50-90 km and 50-160 km beneath Guatemala-El Salvador andNicaragua, respectively. Anomalies observed at the upper part of the slab may be related to dehydration and successive increase inpore pressure in the down-going lithosphere, which may generate volcanism above the anomalies in the upper part of the slab.Anomalies on the lower surface of the Wadati-Benioff zone are likely to be associated with high thermal gradients between theslab and mantle.

Place, publisher, year, edition, pages
2003. Vol. 42, no 4, 575-587 p.
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:uu:diva-90930OAI: oai:DiVA.org:uu-90930DiVA: diva2:163453
Available from: 2003-09-30 Created: 2003-09-30 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Statistical Seismology Studies in Central America: b-value, seismic hazard and seismic quiescence
Open this publication in new window or tab >>Statistical Seismology Studies in Central America: b-value, seismic hazard and seismic quiescence
2003 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[es]
Estudios de Sismología Estadística en Centroamérica : Valor b, amenaza sísmica y quietud sísmica
Abstract [en]

The present thesis collects results of research applying theory and methods of statistical seismology to the seismicity of Central America, a region with a complex tectonic setting controlled by the interaction of four major plates, namely the Caribbean, Cocos, Nazca and North American plates.

Three different earthquake catalogues were used for studies focused on stress in a tectonic volume, seismic hazard maps and seismicity patterns (precursors), covering the region 94ºW to 81ºW and 5ºN to 20ºN.

Variations in the b-value, the parameter in Gutenberg & Richter’s equation LogN=a-bM, as a function of depth in the subduction zone were investigated. High b-values were identified in the upper part of the slab at depths of 80-110km beneath Guatemala-El Salvador and at depths 130-170km beneath Nicaragua. These anomalies may be related to the generation of volcanism occurring above them. Time dependence of the b-value was also studied. Five case studies were selected (events with MS ≥7.2) for a detailed analysis. In three out of five cases, it was possible to link b-value minima to the time of occurrence of corresponding large events.

Seismic quiescence was mapped as a function of time and space by a griding technique. The characteristics of the quiescence were calculated using the statistics Z and ß and for Time Window lengths between 1 and 5 years. Five positive anomalies were found, which can be associated with large earthquakes (MS≥7.2).

Finally, a Monte Carlo approach was utilized to evaluate the ground motion hazard and its uncertainties in northern Central America. A set of new seismic hazard maps exhibiting probabilistic values of peak ground acceleration (PGA) with 50%, 10%, and 5% probabilities of exceedance (PE) in 50 years is presented for a large area of northern Central America, including El Salvador and Guatemala.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2003. 27 p.
Series
Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1104-232X ; 897
Keyword
Geophysics, b-value, seismic hazard, Monte Carlo, seismic quiescence, Central America, stress, Geofysik
National Category
Geophysics
Identifiers
urn:nbn:se:uu:diva-3613 (URN)91-554-5761-4 (ISBN)
Public defence
2003-10-23, Axel Hamberg-salen, Geocentrum, Uppsala, 10:00
Opponent
Supervisors
Available from: 2003-09-30 Created: 2003-09-30 Last updated: 2016-05-13Bibliographically approved

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