Location of the Carlsberg Fault zone from seismic controlled‐source fan recordings

Abstract

We locate the concealed Carlsberg Fault zone in the city of Copenhagen from seismic fan recordings. The fault is part of a fault system close to the border between the Danish Basin and the Baltic Shield. Recent earthquakes indicate that this area is tectonically active. The fault zone is a seismic low‐velocity zone. Fan shots were recorded on three receiver arrays (1.5–2.4 km long arcs) across the fault. Sources were placed inside and up to ∼500 m away from the ∼400–700 m wide fault zone at offsets of up to ∼7 km. Shots inside the fault zone show: 1) weak, delayed first arrivals inside the fault zone; 2) stronger first arrivals outside the fault zone; 3) guided waves inside the fault zone. The fault is a shadow zone for shots detonated outside the fault zone. Our approach facilitates fault mapping in densely urbanized areas where seismic profiling is not feasible.