Go Crystal!! Wonderful blog post. And glad you are teaching the geophysicists what the “red and blue blobs” look like in rock form 😅😉

Thanks to all my collaborators for working together on this piece! I'm excited to see it published. Thanks to #NSF for the funding to conduct this research.
@lsuscience.bsky.social @cascadiaeqs.bsky.social

This doesn’t change the hazard outlook for Cascadia on human timescales — the system is still capable of producing massive earthquakes and tsunamis!! However, the work will inform models of how earthquake ruptures interact with tectonic complexities, such as slab tears and transform boundaries.

All in all, it looks like the Cascadia subduction zone will be getting shorter by ~75 km, or ~8% of its total length. While the Explorer segment is not entirely detached, it is already partially decoupled and well on its way toward subduction cessation.

We think this new 4D framework can explain the pattern of past scenarios where a mid-ocean ridge approaches a trench and subduction terminates and reorganizes into a transform plate boundary. It fits incredibly well with the fossil record of subduction termination along Baja California!

Transforms can fragment the incoming oceanic plate and progressively form microplates, driving diachronous slab tearing, piecewise subduction termination, and triple junction migration.

What does this say about how subduction zones terminate? Transform faults may be a key and overlooked mechanism for past events, such as the Farallon plate breakup and subduction termination preserved along western North America.

The transform boundary formed out of necessity due to resistance to subduction of the warm and buoyant oceanic lithosphere near the RTF triple junction. A trench-perpendicular transform can efficient fragment the incoming oceanic plate and slow its subduction. The tearing pattern is shown here:

The ephemeral transform boundary, called the Nootka Fault Zone which separates the Explorer microplate from the Juan de Fuca Plate, formed as a broad shear zone in rheology homogeneous oceanic lithosphere and progressively localized over time.

The northern oceanic slab is actively tearing apart in multiple directions — a trench-parallel tear propagating from the slab edge, and trench-perpendicular tearing along a unique transform boundary, which causes breakoff of the microplate’s slab, while allowing adjacent subduction to continue.

So what did we find? We focused this study on northern Cascadia which hosts a complex Ridge-Trench-Fault triple junction. New deep-penetrating seismic reflection images and detailed earthquake catalogs reveal the subsurface architecture and evolution during subduction termination.

😍

The beauty of Syros Island in Greece!

Hooray! That’s who I want to connect with

Hahah yes I should’ve made the switch earlier when the big migration happened. Alas I’m here now