Shallow‐Focus Repeating Earthquakes in the Tonga–Kermadec–Vanuatu Subduction Zones

This paper examines moderate shallow‐focus repeating earthquakes along the Tonga–Kermadec–Vanuatu subduction zones by cross‐correlating teleseismically recorded waveforms. A total of 23 clusters and 31 doublets are identified with an average cross‐correlation coefficient of >0.8. A master‐event algorithm is used to determine the precise relative locations. I then estimate and superpose the source areas among these event pairs. This analysis reveals that most of these correlated pairs are repeating earthquakes, which have similar seismic moments (M₀) and completely overlapping source areas. Most of the moderate repeating earthquakes were quasi‐periodic with a recurrence interval (T_r) on the order of years, and occurred at the plate interface. The repeating earthquakes are used to study spatial–temporal variations in fault‐slip rate (⁠⁠) and interplate coupling. Apart from spatial variations in ⁠, a temporal acceleration in is observed, associated with large interplate earthquakes in the Vanuatu region. Interplate coupling is weak for most of the study areas, except the northern section 15°–19° S of the Tonga arc. Strong coupling in the northern Tonga interplate region appears to be at odds with the decoupling expected of a region associated with active back‐arc extension. Repeating earthquakes are also used to examine the scaling relationship between M₀ and T_r derived from the San Andreas fault (SAF). The T_r−M₀ scaling relationship derived from the SAF can adequately account for the normalized T_r for the Kermadec, Vanuatu, and Tonga interplate regions where it is decoupled, suggesting that the convergence rate is the predominant influence on the recurrence interval in a repeating earthquake sequence.