Developing 3D gridded seismicity models in shallow subduction regions: an example from Aotearoa New Zealand
Video not found
Please check back later. Videos are usually posted within 24 hours.
Chris Rollins
GNS Science
- Date & Time
- Location
- Online-only seminar via Microsoft Teams
- Host
- Katherine Guns
- Summary
Statistical spatial earthquake-rate models, such as smoothed seismicity models, are usually done in 2D (mapview). In probabilistic seismic hazard assessment (PSHA), these 2D models are often paired with a 1D depth distribution of earthquakes, or an upper and lower depth. This “2D+1D” approach is often justifiable: catalogued earthquake depths (especially of older events) are often too poorly constrained to justify further model complexity. However, there is one seismically hazardous environment where 2D and 1D models struggle: subduction zones. The 3D nature of subduction zones is actually particularly palpable in PSHA, because upper-plate, subduction-interface and intraslab earthquakes produce very different ground motions and hazards, and so have to be modelled with separate earthquake-rate and ground-motion models. Therefore, subduction zones require 3D earthquake-rate models (even though catalogued event depths are often at their lowest quality in shallow subduction zones because they are almost always offshore).
However, 2D earthquake-rate models are indispensable in their own right: among other advantages, they can represent important earthquakes that predate or lack good depth constraints (e.g., anything before the early to late 20th century, depending on location). The advantages of 2D and 3D models can both be leveraged by replacing the 2D+1D approach with a 2D+3D approach, where the 3D part is a continuously spatially varying earthquake depth-density function (a different 1D depth distribution at each point on the map). In Aotearoa New Zealand, we are working on using this method to pair longer earthquake histories (2D) with representative models of 3D seismotectonic structure, both in Aotearoa’s two subduction zones (Hikurangi-Kermadec and Puysegur) and including volcanic regions and deep sedimentary basins.