Crustal structure and seismicity of the Havre Trough at 26°S

An ocean bottom seismographic (OBS) experiment was carried out to investigate the present‐day tectonics at the northern end of the Havre Trough, a backarc basin in the southwestern Pacific. Hypocenter distribution shows no seismicity within 50 km of the OBS array but two active regions outside the Trough; one is to the northeast of the array at a bathymetric high between the Lau Basin and Havre Trough; the other is to the southeast of the array beneath the landward slope of the Kermadec Trench. P wavespeed structure obtained from the refraction survey is characterized by a thinned island arc crust with a thickness of 9–10 km. Many volcanic intrusions shown in reflection profiles that support extension tectonics are covered by undisturbed sediments. These suggest little present activity related to rifting and/or spreading.