Slow slip in Gisborne, New Zealand
M.S. work of Ryan Yohler
This research focuses on an important aspect of earthquake science called slow‐slip events (SSEs). SSEs are similar to earthquakes but occur more slowly and do not produce damaging seismic energy release. Recently, SSEs have been discovered in areas where large earthquakes happen (the Western United States, Japan, and New Zealand are all examples). The goal of this research is to improve our knowledge of how these events evolve in space and time and their relationship to other seismic phenomena and to quantify the model improvements gained with the addition of seafloor data. Here we investigate a SSE that occurred offshore New Zealand, using both onshore GPS instruments and seafloor pressure instruments (Absolute Pressure Gauges, or APGs) that detect centimeter‐level vertical movement of the seafloor. We found that using seafloor pressure instruments helps to better pinpoint the location and evolution of a SSE offshore of New Zealand in 2014. We also found that these instruments put tighter constraints on the size and timing of the event. This is important because it demonstrates how offshore instruments help further our knowledge of how these events behave, which can inform us about large earthquake hazards in similar subduction zone settings. The results of this study will inform future seafloor instrument deployments to study slow‐slip processes.
Figure 1: Maps of the region of the 2014 Gisborne, New Zealand slow slip event and stations used by Yohler et al., 2019. cGPS refers to land-based continuous GPS sites, APG refers to offshore Absolute Pressure Gauge instruments.
Figure 2: Snapshots of slip rates during the 2014 Gisborne, New Zealand slow slip event. Time advances from top to bottom. The left column is models created using only on-land GPS data; the right column shows models incorporating data from offshore Absolute Pressure Gauge (APG) instruments. Inclusion of APG data helps catch an earlier phase of the slow slip event.
Figure 3: Lower bound models (top row), best fit models (middle row), and upper bound models (bottom row) of slip for the 2014 Gisborne, New Zealand slow slip event. The left column is models created using only on-land GPS data; the right column shows models incorporating data from offshore Absolute Pressure Gauge (APG) instruments. The APG data increases slip in the lower bound model, and decreases slip in the upper bound model, showing that APG data narrows the range of possible models for this slow slip event.