A New Look at Evidence for a Wadati-Benioff Zone and Active Convergence at the North Panama Deformed Belt

The nature of the northern boundary of the Panama microplate, often referred to as the north Panama deformed belt (NPDB), has been the subject of much speculation. Previous studies have used a variety of data, including teleseismic, gravity, bathymetric, marine magnetic, and field studies of uplift and tsunami deposits, as well as modified Mercalli intensity distributions from historic earthquakes to reveal the nature of the NPDB. Data have been collected for over 30 yrs and yet the character of the NPDB remains unclear. Current analyses and interpretation provide a number of mutually exclusive options and much controversy. In this article we examine local and regional seismicity combined with teleseismic observations and historic earthquake data to present an alternative analysis for the NPDB. Using small earthquakes recorded by a local network we image a well-defined Wadati-Benioff zone dipping southward beneath the Panama microplate. These data provide new evidence regarding the nature of Panama microplate-Caribbean plate boundary kinematics and demonstrate the existence of an active subduction zone. A more complete understanding of the nature of the seismicity and plate interactions along the NPDB offshore Panama, including a subduction zone capable of producing earthquakes of M > 7, should be included in future earthquake hazard assessments.