Western US intermountain seismicity caused by changes in upper mantle flow Thorsten W. Becker, Anthony R. Lowry, Claudio Faccenna, Brandon Schmandt, Adrian Borsa, & Chunquan Yu

Study Location N-S trending intermountain belt Marks transition from thin, actively deforming to thicker, less active crust and lithosphere Goal of paper to reveal relationship between rate change of dynamic topography and seismicity—suggests active mantle flow is a major contributor to seismogenic intraplate deformation and topography, while GPE variations have a minor role

Comparison of seismicity and rate change of dynamic topography—suggesting lateral gradients in structure are relevent to where EQ’s happen

Molchan error curves (b) associated skill (metric to measure predictive power of EQ forecasts) Shows lithospheric structure models are poor predictors of seismicity while GPE shows more positive skill—when gradients are considered it flips However—doesn’t really answer question, only used as a comparison

Extended data figure 1(a-c,e) Moho sometimes aligns with seismicity but areas above the Snake River Plain and Yellowstone, becomes less correlative

e&f—regions with highest rate change of dynamic topography corresponds to the gradient in dynamic topography Fig3—inferred temperature anomalies and mantle flow velocity (background—corresponds to e) and temporal changes (foreground—corresponds to f)

Both upwelling and downwelling mantle anomalies can produce a positive rate change for dynamic topography Upward push of rising anomalies increase dynamic topo, singing of a negative anomaly reduces negative dynamic topo Fig 1a (Braun, 2010)

Surface dynamic topography Temporal change Shallow, hot Shallow, cold

Surface dynamic topography Temporal change Deep, hot Extended data figure 6—notice rate change of dynamic topo is positive for both cold/sinking and hot/rising because of the reduction of negative and increase of positive dynamic topography Shallow, hot

Considerations not included in study: Erosion Magmatic intrusions Changes in vertical normal stress from mantle convection + modulation from lithospheric structure might explain intermountain seismicity Intraplate seismicity may require disequilibrium perturbation to a system already in a critical state Extended data figure 7—simplified, linear, multivariable regression implies both GPE and structural gradients contribute positively—but may play minor part in driving seismicity in this region (figure 2b) Considerations not included in study: Erosion Magmatic intrusions Tectonic shortening Rifting Compositional anomalies