Fig. 1: Distribution of slip modes and related tectonic structures in Nankai Trough and Costa Rica.
a Distribution of slow earthquakes along the Nankai Trough in SW Japan showing tectonic tremor distinguished as shallow very low frequency earthquakes (VLFs) and deep tremor11, co-seismic megathrust rupture2 and slow-slip events (SSEs)2 compared to the location of subducted seamounts and magmatic bodies intruded within the accretionary prism56,66, the subducted Kyushu Ridge67, and the subducted paleo-Zenisu Ridge66. Inset: Number of non-volcanic tremors and occurrence of SSEs in 2008 between 136°E and 137°E longitude (from: “Slow Earthquake Database” http://www-solid.eps.s.u-tokyo.ac.jp/~sloweq/68). One degree of latitude is 111.11 km. b Distribution of slow earthquakes offshore Costa Rica compared to subducted seamounts69,70. Embayment in the forearc is assumed to be left by subducted seamounts69. Seismic and GPS data are here limited to the Nicoya Peninsula. The location of the outcrops of Osa Mélange referred in the text as well as IODP Site 344-U1414 are also shown in the map. One degree of latitude is 111.11 km.
