Deep Short‐Term Slow Slip and Tremor in the Manawatu Region, New Zealand.

The Manawatu region experiences deep tremor and long‐term slow slip events (SSEs); however, tremor is adjacent to, and not co‐located with, long‐term SSEs. Observations of episodic tremor and slip (ETS) elsewhere suggest it is possible smaller short‐term SSEs below the current detection threshold occur where tremor is observed. Therefore, we sought to determine if small SSEs occurred with Manawatu tremor. We decomposed GNSS data using times of tremor to assess average surface displacements and performed a static slip inversion to model the displacement during tremor. The slip inversion suggested small slow slip partially coincided with tremor and long‐term SSEs may influence these small SSEs by increasing slip rates. We suggest that the interface below deep long‐term SSEs may slip often, in small ETS‐like SSEs that are not individually detectable geodetically. The question remains as to the nature of the strong variability in SSE behavior with depth and duration in the southern Hikurangi margin. Plain Language Summary: In between the Earth's tectonic plates, energy builds over time and can be released along faults suddenly (seconds‐minutes; i.e., earthquakes) or slowly (weeks‐years; i.e., slow slip events). Slow slip often happens with low‐frequency earthquakes (i.e., tectonic tremor). The North Island, New Zealand features two colliding tectonic plates with the potential to generate large earthquakes. The interface between these plates has both deep tectonic tremor and large, long‐lasting slow slip, but the tectonic tremor is deeper on the fault than the large slow slip. Studies have suggested small, short‐lasting slow slip, usually not able to be detected, occur where tectonic tremor is found. In this study we tried a different approach to find the small slow slip. While small slow slip are not detected by themselves, we were able to detect their cumulative effect in the tectonic tremor area. We modeled small slow slip during tectonic tremor to find the mean sliding rate on the fault that is between the tectonic plates. The large long‐lasting slow slip may drive this smaller slow slip by making them slip faster. The question remains as to the cause of the many types of slow slip in New Zealand. Key Points: GNSS data indicates newly detected short‐term slow slip in region of deep tremorLong‐term slow slip events may influence these small slow slip events by increasing slip ratesThree types of slow slip overlap along‐strike in Hikurangi margin: shallow, short‐term; deep, long‐term; deeper, short‐term with tremor [ABSTRACT FROM AUTHOR]