Seismicity of the Caribbean‐Nazca Boundary: Constraints on microplate tectonics of the Panama region

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Abstract
There are at least three kinds of models that have been used to explain plate motions and boundaries in the Panama region. These models suggest that the major Caribbean‐Nazca boundary is (1) a thrust fault along which the Panama Deformed Belt has developed, (2) a left‐lateral strike‐slip fault along the southern margin of Panama, or (3) a diffuse array of mostly thrust faults which cause internal deformation to occur throughout Panama. In this paper, we use joint epicenter location methods to obtain improved locations for earthquakes that occurred in this region between 1964 and 1985 and we use waveform modeling to obtain more precise depths for five events. Hypocenters of 13 events beneath the Panama Deformed Belt suggest that overthrusting of Panama upon the Caribbean plate causes active deformation which supports model 1 but does not rule out models 2 and 3. The nature of seismic faulting along the Panama Deformed Belt is complex and supports the premise that slow north‐south convergence loads the cold thick Caribbean lithosphere and causes it to fail seismically. Epicenters of 64 events along the Panama Fracture Zone indicate that this north–south trending rightlateral transform fault is splayed north of 6°N. Overall, the seismicity throughout suggests that the Panama arc can be treated as a microplate, in accordance with models 1 or 2. Similarly, a possible second microplate may exist south of Panama, but if so it does not affect regional plate motions significantly. The strongest evidence for model 3 occurs in the easternmost and westernmost portions of Panama, where the diffuse seismicity prevents us from resolving specific microplate triple‐junction boundaries.