Fig. 3
a, b Heat flow measurements over subduction zones show a marked low heat flow in the forearc, transitioning to higher and more scatted observations in the arc and backarc (where the slab is at a depth of greater than 80 km). a Heat flow measurements for Tohoku. Solid blue triangles show average heat flow for Tohoku as a function of trench distance; solid circles: same but now for heat flow measurements within 100 km distance from the profile T18 from van Keken et al. (2002) shown in Fig. 1. b Heat flow measurements from the global heat flow database (see Pollack et al. 1993, and https://www.geophysik.rwth-aachen.de/IHFC/heatflow.html) near the CAFE profile in Cascadia (Abers et al. 2009). The high heat flow near the trench is due to the young age of the subducting lithosphere. c–e Seismic attenuation studies in Central Alaska (modified from Stachnik et al. 2004) show a sharp transition between attenuating properties of the forearc and arc/backarc mantle c Waveforms observed for an earthquake recorded in a station over the arc. d Same as c but now for waveforms obtained for the same earthquake by a station located over the forearc. Note the significant change in amplitude scale as well as the change in frequency content of the waveforms between the two recordings. e Attenuation tomography showing a sharp transition between high Q in the forearc mantle wedge and low Q elsewhere. Raypaths of the earthquake to stations with waveforms recorded as shown in panel c and d are schematically indicated with the arrows