Teleseismic attenuation, temperature, and melt of the upper mantle in the Alaska subduction zone

Abstract

Plain Language Summary Seismic waves lose more energy passing through hot and partly molten volumes than cold regions. As a result, measurements of variation in their amplitudes, or attenuation, provides a tool for mapping out the upper mantle, complementing more traditional measurements of their variation in travel time. New high-quality arrays across southern Alaska, along with recent methodological developments, now allow this measurement to be made systematically across the entire region. They show consistently low attenuation where subducting plates are near the surface or along paths that follow the cold subducting plates. These regions are in southernmost Alaska. By contrast, signals traveling beneath volcanic regions or north of them, where hot mantle flows toward subduction zones, show high attenuation. The attenuation patterns resemble those from travel time, but seem to show more sensitivity to the upper 150 km of the Earth while travel time delays more uniformly sample deeper. Sedimentary basins show confusing signals, with travel time delays as expected for low-wavespeed sediments, but high amplitudes that are difficult to explain. These signals allow quantitative mapping of temperature and melt variations in the upper mantle, even in regions as complex as subduction zones where both properties vary rapidly over short distances.SOTO CASTANEDA ET AL.

Variable Depths of Magma Genesis in the North China Craton and Central Asian Orogenic Belt Inferred From Teleseismic P Wave Attenuation

“…The strong anti‐correlation between attenuation and velocity is consistent with the sensitivity of both to temperature, and possibly melt and water (e.g., Cammarano et al., 2003; Goes et al., 2000). These observations support previous inferences that teleseismic attenuation is primarily sensitive to the subcrustal lithosphere‐asthenosphere system (Bezada & Smale, 2019; Byrnes & Bezada, 2020; Kennett & Abdullah, 2011), while studies based on seismic velocity can interrogate structure within the crust and below the asthenosphere (Soto Castaneda et al., 2021). Additionally, assuming a typical crust with thickness of 35–40 km, the travel time of P wave in the crust will be around 5 s. We therefore estimate that even if Qp in the crust is as low as in the asthenosphere (Qp = 150), we only get a $${\Delta}{t}^{\ast }$$ of 0.03–0.04 s, which is within the error of the model in this study.…”

Subduction of an Oceanic Plateau Across Southcentral Alaska: Scattered‐Wave Imaging

“…Some tomographic studies of the region show a faint high‐velocity anomaly at mantle depths in the Wrangell segment that has been interpreted as subducting material as far east as 140°W (e.g., Feng and Ritzwoller., 2019; Gou et al., 2019; Jiang et al., 2018), but other studies see no such anomaly (e.g., Eberhart‐Phillips et al., 2006; Martin‐Short et al., 2018, 2016; Nayak et al., 2020). Teleseismic attenuation indicates an attenuating arc/backarc and low‐attenuation forearc, consistent with subduction (Soto Castañeda et al., 2021). Overall, the accommodation of convergence east of 146°W is poorly defined and the nature of subduction of the Yakutat terrane across southcentral Alaska is poorly documented (Eberhart‐Phillips et al., 2006; Elliott et al., 2013; Elliott & Freymueller, 2020).…”

“… Map of the study region. Inset maps show location of teleseismic earthquakes during each temporary array deployment: left inset map–BEAAR array 6/2000–7/2001 (Ferris et al., 2003), middle inset map–MOOS array 6/2007–10/2008 (Li et al., 2013), right inset map–WVLF array 6/2016–5/2018 (Soto Castañeda et al., 2021). Color of earthquakes in inset maps match corresponding station arrays: Orange–BEAAR, Green–MOOS, Blue–WVLF.…”

“…This study uses data from the Wrangell Volcanism and Lithospheric Fate (WVLF) experiment (https://doi.org/10.7914/SN/YG_2016; Soto Castañeda et al., 2021), which deployed 36 broadband seismometers across the eastern half of southcentral Alaska from June 2016 to July 2018 (Figure 1). In addition, this study uses data from previous temporary deployments, namely the Broadband Experiment Across the Alaska Range (BEAAR; Ferris et al., 2003) and Multidisciplinary Observations of Onshore Subduction (MOOS; Li et al., 2013), along with Transportable Array (TA; Ruppert & West, 2020), the Alaska Earthquake Center Network, and other local network stations.…”

Subduction of an Oceanic Plateau Across Southcentral Alaska: High‐Resolution Seismicity

“…Southcentral Alaska is strongly influenced by the subduction and accretion of the Yakutat terrane, an oceanic plateau that collided with the North American plate 12–30 Mya (Christeson et al., 2010; Finzel et al., 2011; Plafker et al., 1994). The Yakutat terrane is imaged by offshore active‐source seismic reflection and refraction (Christeson et al., 2010; Fuis et al., 2008; Worthington et al., 2012) and onshore west of 147°W by a well‐defined highly active Alaska‐Aleutian Wadati‐Benioff zone (WBZ; Page et al., 1989; Ratchkovski & Hansen, 2002; Stephens et al., 1984), tomography (Eberhart‐Phillips et al., 2006; Gou et al., 2019; Jiang et al., 2018; Martin‐Short et al., 2016, 2018; Yang & Gao, 2020), receiver functions (e.g., Ferris et al., 2003; Kim et al., 2014; Rondenay et al., 2008, 2010; Rossi et al., 2006), and attenuation (e.g., Soto Castaneda et al., 2021; Stachnik et al., 2004). Volcanism is continuous from the Aleutian arc to southcentral Alaska, where it is nearly absent in the Denali volcanic gap (DVG) despite the subducting slab and mantle wedge having characteristics consistent with magma generation (Eberhart‐Phillips et al., 2006; McNamara & Pasyanos, 2002; Stachnik et al., 2004).…”