SEISMOTECTONIC CONSTRAINTS ON THE CONVERGENCE RATE BETWEEN THE RIVERA AND NORTH-AMERICAN PLATES

There are two significantly different types of models for the convergence rate between the Rivera and North American plates. The first type, the high-rate model (Bandy, 1992), predicts convergence rates of approximately 5.0 cm/yr near the southern end of the Rivera-North America subduction zone and between 2.0 and 3.0 cm/yr at its northern end. Tn contrast, the second type, the low-rate model (e.g., DeMets and Stein, 1990), predicts convergence rates of between 2.0 and 3.3 cm/yr near the southern end of the Rivera-North America subduction zone and between 0.6 and 1.7 cm/yr at its northern end. Seismotectonic relationships, which relate seismic characteristics of subduction zones (maximum magnitudes, maximum seismic depths, etc.) to plate tectonic parameters (convergence rates, age of the oceanic lithosphere, etc.) provide a means of distinguishing between the two different models. Three such relationships suggest that the Rivera-North American and Cocos-North American convergence rates should be roughly equal across the Rivera-Cocos plate boundary, favoring the high-rate model. Employing the high-rate model, one can evaluate the magnitude and distribution of the strike-slip component of forearc motion, V-ss, produced by oblique convergence between the Rivera and North American plates. The analysis indicates both a progressive increase and clockwise reorientation of V-ss northwestward along the plate contact zone of the Rivera-North America subduction zone. Such a distribution in V-ss should produce a northwestward movement of and NW-SE oriented extension within the interior of the Jalisco Block, consistent with previous proposals of Jalisco Block motions. Also, such a distribution in V-ss should produce a slight clockwise rotation of the Jalisco Block in the vicinity of Bahia de Banderas, consistent with paleomagnetic data.