GPS measurements of crustal deformation associated with the 22 April 1991, Valle de la Estrella, Costa Rica Earthquake

Abstract

We present analysis results for Global Positioning System (GPS) measurements made at sites in Costa Rica during two campaigns in February and July 1991. GPS solutions for 5 sites (Limon, Liberia, Bratsi, ETCG, and Vueltas) reveal significant horizontal and vertical displacements relative to their February positions. Horizontal displacements relative to Liberia, measured 244.7 ± 0.8, 89.2 ± 0.9, 12.4 ± 1.3, and 1.9 ± 0.9 cm at Limon, Bratsi, Vueltas, and ETCG respectively. Vertical displacements relative to Liberia measured 163 ± 2.1, 15.3 ± 3.0, −10.5 ± 4.4, and −0.6 ±2.1 cm at Limon, Bratsi, Vueltas, and ETCG respectively. We find differences in the GPS derived vertical and horizontal displacements compared to other types of geodetic measurements of uplift in the coastal region and their associated models. To address these differences we compute a dislocation model which fits the GPS measured displacements. A simple uniform planar slip model can not reconcile the differences between the coastal uplift data or the seismic moment, suggesting considerable complexity of the earthquake source.

Kinematics of the western Caribbean: Collision of the Cocos Ridge and upper plate deformation

“…We present a new 154 site, GPS‐derived interseismic surface velocity field in Central America and northwestern South America based on measurements spanning the period 1993–2012 (Figure ; Table S1). We utilized new GPS data collected at sites, where data existed from previous studies [e.g., Lundgren et al ., ; Trenkamp et al ., ; Norabuena et al ., ; Turner et al ., ; LaFemina et al ., ; Mora et al ., ], and from episodic and continuous GPS sites installed as part of this study. These GPS data sets were processed together with GIPSY‐OASIS II version 5.1 in precise point positioning mode, using standard clock and satellite ephemeris data from the Jet Propulsion Laboratory [ Zumberge et al ., ] for consistent analysis.…”

Fore‐arc motion and Cocos Ridge collision in Central America

“…The Caribbean plate is underthrusting Central America along the North Panama Deformed Belt (NPDB). Large magnitude ( M > 7.0) historical thrust earthquakes have occurred repeatedly along the NPDB (Figure 1) [ Plafker and Ward , 1992; Goes et al , 1993; Lundgren et al , 1993; Tajima and Kikuchi , 1995].…”

“…Our GPS velocity field is based on episodic (E) and continuous (C) GPS observations and resultant time series spanning the period 1993–2005. We combine EGPS data sets presented by Lundgren et al [1993, 1999], Trenkamp et al [2002], Norabuena et al [2004], and Turner et al [2007] with new EGPS and CGPS data to define the secular velocity field for this time period. All data were reprocessed in a consistent reference frame (ITRF00) (Table 1) using GIPSY‐OASIS II [ Zumberge et al , 1997] following the methods of Sella et al [2002].…”

Geodetic and seismic constraints on some seismogenic zone processes in Costa Rica

“…In southern Costa Rica, elastic and permanent deformation (shortening) also occur in the back‐arc region, on and near the North Panama deformed belt, a fold and thrust belt marking the boundary between the Caribbean plate and the Panama block [ Case and Holcomb , 1980; Adamek et al , 1987; Vergara‐Munoz , 1988; Silver et al , 1990, 1995] (Figures 1 and 2). The 1991 M w = 7.6 Valle de Estrella earthquake was a thrust fault earthquake on a southwest dipping fault defining the northeast corner of the belt, indicating that this boundary is active [ Plafker and Ward , 1992; Goes et al , 1993; Lundgren et al , 1993; Protti and Schwartz , 1994]. Determining the long‐term angular velocity of a separate Panama block relative to the Caribbean and Cocos plates is difficult with the current sparse data set.…”