Opposite Faulting in Global Seismicity

Abstract The recent observation of neighboring earthquakes with anti-correlated waveforms, referred to as anti-repeating earthquakes, or anti-repeaters, suggests that almost opposite fault slip may occur consecutively along the same or nearby structures in Earth. These earthquakes have so far been identified in a few areas only, although involving different seismogenic contexts, like tectonic, volcanic, and induced seismicity, so they could be a more common phenomenon than previously thought. Here, we analyze large and moderate-sized earthquakes worldwide in a systematic manner, scanning the Global Centroid Moment Tensor catalog over 48 yr in search of pairs of earthquakes with neighboring centroid locations and nearly opposite moment tensors. The results are somewhat surprising: thousands of nearby earthquake pairs with opposite source orientations can be found, clustering at hundreds of locations on Earth, occurring at different depths, in different tectonic settings, as well as in volcanic environments. We validate the detections by their waveform anti-correlation and report a global catalog of opposite faulting, as a first atlas for this new type of seismological observation.