The thermal regime of continental lithosphere plays a fundamental role in controlling the behavior of tectonic plates. In this work, we assess the thermal state of the North American upper mantle by combining shear-wave velocity models calculated using data from the EarthScope facility with empirically-derived anelasticity models and basalt thermobarometry. We estimate the depth to the thermal lithosphere-asthenosphere boundary (LAB), defined as the intersection of a geotherm with the 1300° C adiabat. Results show lithospheric thicknesses across the contiguous US vary between ~40 km and > 200 km. The thinnest thermal lithosphere is observed in the tectonically active western US and the thickest lithosphere in the mid-continent. By combining geotherm estimates with solidus curves for peridotite, we show that a pervasive partial melt zone is common within the western US upper mantle and that partial melt is absent in the eastern and central US without significant metasomatism.

The 2019 Museum Fire burned in a mountainous region near the city of Flagstaff, AZ, USA. Due to the high risk of post-wildfire debris flows and flooding entering the city, we deployed a network of seismometers within the burn area and downstream drainages to examine the efficacy of seismic monitoring for post-fire flows. Seismic instruments were deployed during the 2019, 2020, and 2021 monsoon seasons following the fire and recorded several debris flow and flood events, as well as signals associated with rainfall, lighting and wind. Signal power, frequency content, and wave polarization were measured for multiple events and compared to rain gauge records and images recorded by cameras installed in the study area. We use these data to demonstrate the efficacy of seismic recordings to (1) detect and differentiate between different energy sources, (2) estimate the timing of lightning strikes, (3) calculate rainfall intensities, and (4) determine debris flow timing, size, velocity, and location. This work confirms the validity of theoretical models for interpreting seismic signals associated with debris flows and rainfall in post-wildfire settings and demonstrates the efficacy of seismic data for identifying and characterizing debris flows.