Integrated seismic interpretation of the Carlsberg Fault zone, Copenhagen, Denmark

TY - JOUR

T1 - Integrated seismic interpretation of the Carlsberg Fault zone, Copenhagen, Denmark

AU - Nielsen, Lars

AU - Thybo, Hans

AU - Jørgensen, Mette Iwanouw

N1 - doi:10.1111/j.1365-246X.2005.02664.x

PY - 2005

Y1 - 2005

N2 - We locate the concealed Carlsberg Fault zone along a 12-km-long trace in the Copenhagen city centre by seismic refraction, reflection and fan profiling. The Carlsberg Fault is located in a NNW-SSE striking fault system in the border zone between the Danish Basin and the Baltic Shield. Recent earthquakes indicate that this area is tectonically active. A seismic refraction study across the Carlsberg Fault shows that the fault zone is a low-velocity zone and marks a change in seismic velocity structure. A normal incidence reflection seismic section shows a coincident flower-like structure. We have recorded seismic signals in a fan geometry from shots detonated both inside the low-velocity fault zone and up to ~500 m away from the fault zone. The seismic energy was recorded on three receiver arrays (1.5- to 2.4-km-long arcs) across the expected location of the ~400- to 700-m-wide fault zone at distances of up to ~7 km from the shots. Shots detonated inside the fault zone result in (1) weak and delayed first arrivals on the receivers located inside the fault zone compared to earlier and stronger first arrivals outside the fault zone; (2) strong guided P and S waves as well as surface waves inside the fault zone. The fault zone is a shadow zone to shots detonated outside the fault zone. Finite-difference wavefield modelling supports the interpretations of the fan recordings. Our fan recording approach facilitates cost-efficient mapping of fault zones in densely urbanized areas where seismic normal incidence and refraction profiling are not feasible.

AB - We locate the concealed Carlsberg Fault zone along a 12-km-long trace in the Copenhagen city centre by seismic refraction, reflection and fan profiling. The Carlsberg Fault is located in a NNW-SSE striking fault system in the border zone between the Danish Basin and the Baltic Shield. Recent earthquakes indicate that this area is tectonically active. A seismic refraction study across the Carlsberg Fault shows that the fault zone is a low-velocity zone and marks a change in seismic velocity structure. A normal incidence reflection seismic section shows a coincident flower-like structure. We have recorded seismic signals in a fan geometry from shots detonated both inside the low-velocity fault zone and up to ~500 m away from the fault zone. The seismic energy was recorded on three receiver arrays (1.5- to 2.4-km-long arcs) across the expected location of the ~400- to 700-m-wide fault zone at distances of up to ~7 km from the shots. Shots detonated inside the fault zone result in (1) weak and delayed first arrivals on the receivers located inside the fault zone compared to earlier and stronger first arrivals outside the fault zone; (2) strong guided P and S waves as well as surface waves inside the fault zone. The fault zone is a shadow zone to shots detonated outside the fault zone. Finite-difference wavefield modelling supports the interpretations of the fan recordings. Our fan recording approach facilitates cost-efficient mapping of fault zones in densely urbanized areas where seismic normal incidence and refraction profiling are not feasible.

KW - Faculty of Science

KW - seismisk

KW - Danmark

KW - Carlsberg forkastelsen

KW - seismic

KW - Denmark

KW - Carlsberg Fault

U2 - 10.1111/j.1365-246X.2005.02664.x

DO - 10.1111/j.1365-246X.2005.02664.x

M3 - Journal article

SN - 0956-540X

SP - 461

EP - 478

JO - Geophysical Journal International

JF - Geophysical Journal International

IS - 162

ER -