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Constraining Slow Slip in Cascadia Using a Joint Tremor-GNSS Inversion

Description: 

In the Cascadia subduction zone, slow slip events (SSEs) are episodes of aseismic fault slip that occur over days to months without producing significant earthquakes. Geodetic data constrain SSE slip through quasi-static inversions at daily to longer timescales, but lack the temporal resolution needed to resolve short-timescale variations in slip. In contrast, tremor, a superposition of low-frequency earthquakes (LFEs), provides insight into slip at much shorter timescales. However, employing LFEs to directly constrain the time history of fault slip is fundamentally challenging. The amount of slip associated with individual LFEs is poorly constrained, LFE locations are uncertain at the scale of the slipping fault, and their source dimensions are orders of magnitude smaller than the areas over which slip is typically inferred. Moreover, it remains unclear how individual LFEs relate to surrounding aseismic slip. As a result, existing LFE catalogs are incomplete and difficult to interpret physically, with overlapping sources and low-amplitude events complicating the relation between observed seismicity and underlying fault slip.
Here, we develop a framework that leverages the relationship between continuous seismic noise amplitude and underlying LFE rates, allowing tremor amplitudes to function as a proxy for time-varying slip rates. We validate our technique using synthetic tremor generated by systematically varying LFE rates to determine how changes in tremor amplitude reflect changes in underlying slip. This relationship is then applied to real seismic data from individual stations. Finally, we develop a joint inversion in which tremor-derived slip rate estimates serve as dynamic constraints to complement static GNSS displacements, allowing the spatiotemporal evolution of slow slip to be resolved more fully. By integrating tremor-based slip rates over short time windows, this approach aims to recover recorded GNSS displacements while resolving the temporal and spatial evolution of slow slip that geodetic or catalog-based seismic data alone cannot achieve.

Session: SSJ-SSOC-SSA Joint Session: From Slow to Fast Earthquakes: Bridging the Spectrum of Fault Slip [Poster]

Type: Poster

Date: 4/16/2026

Presentation Time: 08:00 AM (local time)

Presenting Author: Lois Papin

Student Presenter: Yes

Invited Presentation: 

Poster Number: 149

Authors