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Estimates of Seismic Moment Accumulation Rate from Geodesy

David T. Sandwell, Katherine A. Guns, Xiaohua Xu, Yehuda Bock, & Bridget R. Smith-Konter

Submitted September 10, 2023, SCEC Contribution #13160, 2023 SCEC Annual Meeting Poster #060

Measuring the accumulation of seismic moment on locked faults is a key element of assessing seismic hazard. There are two basic approaches to estimating moment accumulation from geodesy; fault-based modeling and regional strain rate-based estimation. Each approach has its strengths and weaknesses. The main advantage of calculating moment from strain rate is that moment is a map of the stored elastic energy of each Kostrov cell and thus does not rely on fault geometry. Moreover, it does not distinguish between on- and off-fault moment accumulation. The main disadvantages are: 1) the calculation of strain rate from geodetic velocities (GNSS and/or InSAR) is highly non-unique because one must grid the three components of velocity and then take the spatial gradient which amplifies both the signal and noise (Maurer and Materna, 2023) and 2) The Kostrov thickness times the shear modulus is an unknown parameter.

The main purpose of this study is to compare the two approaches and develop best practices and realistic bounds for estimating seismic moment accumulation rate from geodesy and ancillary data. The main findings are: 1) A comparison of published fault-based and strain-rate based models for moment accumulation show the thickness of the Kostrov layer is 7.3 – 11.5 km. 2) Differences between strain-rate moment estimates of observed data and fault-based moment estimates suggest that 32-54% of seismic moment accumulates away from known faults. 3) There is a major uncertainty in strain-rate based moment related to the various methods used to estimate strain rate from geodetic data.

Sandwell, D. T., Guns, K. A., Xu, X., Bock, Y., & Smith-Konter, B. R. (2023, 09). Estimates of Seismic Moment Accumulation Rate from Geodesy. Poster Presentation at 2023 SCEC Annual Meeting.

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