Acknowledgments We thank all those involved in the deployment of the nBOSS seismic array. BMKG and ITB facilitated the deployment of the Kalimantan array; without them, the stations could not have been deployed. nBOSS seismometers were provided by the University of Cambridge, University of Aberdeen, and SEIS-UK (Loan 1038). Many thanks go to Nick Harmon and Yingje Yang, both of whom provided vital software. Many figures were made using GMT (Wessel et al., 2019). TG is funded by a Leverhulme Early Career Research Fellowship (ECF-049). SP acknowledges support from the Natural Environmental Research Council (NERC) Grant NE/R013500/1 and from the European Union's Horizon 2020 Research and Innovation Program under Marie Skłodowska-Curie Grant Agreement 790203. Earth Sciences Cambridge publication number ESC-6308. ; Peer reviewed ; Publisher PDF