We discuss the subsurface structure of the Karadere-Duzce branch of
the North Anatolian Fault based on analysis of a large seismic data
set recorded by a local PASSCAL network in the 6 months following
the Mw= 7.4 1999 Izmit earthquake. Seismograms observed at stations
located in the immediate vicinity of the rupture zone show motion
amplification and long-period oscillations in both P- and S-wave
trains that do not exist in nearby off-fault stations. Examination
of thousands of waveforms reveals that these characteristics are
commonly generated by events that are well outside the fault zone.
The anomalous features in fault-zone seismograms produced by events
not necessarily in the fault may be referred to generally as fault-zone-related
site effects. The oscillatory shear wave trains after the direct
S arrival in these seismograms are analysed as trapped waves propagating
in a low-velocity fault-zone layer. The time difference between the
S arrival and trapped waves group does not grow systematically with
increasing source-receiver separation along the fault. These observations
imply that the trapping of seismic energy in the Karadere-Duzce rupture
zone is generated by a shallow fault-zone layer. Traveltime analysis
and synthetic waveform modelling indicate that the depth of the trapping
structure is approximately 3-4 km. The synthetic waveform modelling
indicates further that the shallow trapping structure has effective
waveguide properties consisting of thickness of the order of 100
m, a velocity decrease relative to the surrounding rock of approximately
50 per cent and an S-wave quality factor of 10-15. The results are
supported by large 2-D and 3-D parameter space studies and are compatible
with recent analyses of trapped waves in a number of other faults
and rupture zones. The inferred shallow trapping structure is likely
to be a common structural element of fault zones and may correspond
to the top part of a flower-type structure. The motion amplification
associated with fault-zone-related site effects increases the seismic
shaking hazard near fault-zone structures. The effect may be significant
since the volume of sources capable of generating motion amplification
in shallow trapping structures is large.
Department of Earth Sciences, University of Southern CA, Los Angeles,
CA 90089-0740, USA. E-mail: benzion@terra.usc.edu; NY 10964,; 34850,;
United States Geological Survey, MS 977, 345 Middlefield Rd, Menlo
Park, CA 94025, USA; 81220
%0 Journal Article
%1 ben-zion_etal:2003
%A Ben-Zion, Yehuda
%A Peng, Zhigang
%A Okaya, David
%A Seeber, Leonardo
%A Armbruster, John G.
%A Ozer, Naside
%A Michael, Andrew J.
%A Baris, Serif
%A Aktar, Mustafa
%C Department of Earth Sciences, University of Southern CA, Los Angeles,
CA 90089-0740, USA. E-mail: benzion@terra.usc.edu; NY 10964,; 34850,;
United States Geological Survey, MS 977, 345 Middlefield Rd, Menlo
Park, CA 94025, USA; 81220
%D 2003
%J Geophysical Journal International
%K geophysics seismology
%N 3
%P 699--717
%R 10.1046/j.1365-246X.2003.01870.x
%T A shallow fault-zone structure illuminated by trapped waves in the
Karadere-Duzca branch of the North Anatolian Fault, western Turkey
%U http://dx.doi.org/10.1046/j.1365-246X.2003.01870.x
%V 152
%X We discuss the subsurface structure of the Karadere-Duzce branch of
the North Anatolian Fault based on analysis of a large seismic data
set recorded by a local PASSCAL network in the 6 months following
the Mw= 7.4 1999 Izmit earthquake. Seismograms observed at stations
located in the immediate vicinity of the rupture zone show motion
amplification and long-period oscillations in both P- and S-wave
trains that do not exist in nearby off-fault stations. Examination
of thousands of waveforms reveals that these characteristics are
commonly generated by events that are well outside the fault zone.
The anomalous features in fault-zone seismograms produced by events
not necessarily in the fault may be referred to generally as fault-zone-related
site effects. The oscillatory shear wave trains after the direct
S arrival in these seismograms are analysed as trapped waves propagating
in a low-velocity fault-zone layer. The time difference between the
S arrival and trapped waves group does not grow systematically with
increasing source-receiver separation along the fault. These observations
imply that the trapping of seismic energy in the Karadere-Duzce rupture
zone is generated by a shallow fault-zone layer. Traveltime analysis
and synthetic waveform modelling indicate that the depth of the trapping
structure is approximately 3-4 km. The synthetic waveform modelling
indicates further that the shallow trapping structure has effective
waveguide properties consisting of thickness of the order of 100
m, a velocity decrease relative to the surrounding rock of approximately
50 per cent and an S-wave quality factor of 10-15. The results are
supported by large 2-D and 3-D parameter space studies and are compatible
with recent analyses of trapped waves in a number of other faults
and rupture zones. The inferred shallow trapping structure is likely
to be a common structural element of fault zones and may correspond
to the top part of a flower-type structure. The motion amplification
associated with fault-zone-related site effects increases the seismic
shaking hazard near fault-zone structures. The effect may be significant
since the volume of sources capable of generating motion amplification
in shallow trapping structures is large.
@article{ben-zion_etal:2003,
abstract = {We discuss the subsurface structure of the Karadere-Duzce branch of
the North Anatolian Fault based on analysis of a large seismic data
set recorded by a local PASSCAL network in the 6 months following
the Mw= 7.4 1999 Izmit earthquake. Seismograms observed at stations
located in the immediate vicinity of the rupture zone show motion
amplification and long-period oscillations in both P- and S-wave
trains that do not exist in nearby off-fault stations. Examination
of thousands of waveforms reveals that these characteristics are
commonly generated by events that are well outside the fault zone.
The anomalous features in fault-zone seismograms produced by events
not necessarily in the fault may be referred to generally as fault-zone-related
site effects. The oscillatory shear wave trains after the direct
S arrival in these seismograms are analysed as trapped waves propagating
in a low-velocity fault-zone layer. The time difference between the
S arrival and trapped waves group does not grow systematically with
increasing source-receiver separation along the fault. These observations
imply that the trapping of seismic energy in the Karadere-Duzce rupture
zone is generated by a shallow fault-zone layer. Traveltime analysis
and synthetic waveform modelling indicate that the depth of the trapping
structure is approximately 3-4 km. The synthetic waveform modelling
indicates further that the shallow trapping structure has effective
waveguide properties consisting of thickness of the order of 100
m, a velocity decrease relative to the surrounding rock of approximately
50 per cent and an S-wave quality factor of 10-15. The results are
supported by large 2-D and 3-D parameter space studies and are compatible
with recent analyses of trapped waves in a number of other faults
and rupture zones. The inferred shallow trapping structure is likely
to be a common structural element of fault zones and may correspond
to the top part of a flower-type structure. The motion amplification
associated with fault-zone-related site effects increases the seismic
shaking hazard near fault-zone structures. The effect may be significant
since the volume of sources capable of generating motion amplification
in shallow trapping structures is large.},
added-at = {2012-09-01T13:08:21.000+0200},
address = {Department of Earth Sciences, University of Southern CA, Los Angeles,
CA 90089-0740, USA. E-mail: benzion@terra.usc.edu; NY 10964,; 34850,;
United States Geological Survey, MS 977, 345 Middlefield Rd, Menlo
Park, CA 94025, USA; 81220},
author = {Ben-Zion, Yehuda and Peng, Zhigang and Okaya, David and Seeber, Leonardo and Armbruster, John G. and Ozer, Naside and Michael, Andrew J. and Baris, Serif and Aktar, Mustafa},
biburl = {https://www.bibsonomy.org/bibtex/20ca06ced10fb193476087b90ff3e5815/nilsma},
doi = {10.1046/j.1365-246X.2003.01870.x},
interhash = {e7302e1b4d2c81fd95f14f8eeee3f8b6},
intrahash = {0ca06ced10fb193476087b90ff3e5815},
issn = {1365-246X},
journal = {Geophysical Journal International},
keywords = {geophysics seismology},
month = mar,
number = 3,
pages = {699--717},
timestamp = {2021-02-09T13:22:13.000+0100},
title = {A shallow fault-zone structure illuminated by trapped waves in the
Karadere-Duzca branch of the North Anatolian Fault, western Turkey},
url = {http://dx.doi.org/10.1046/j.1365-246X.2003.01870.x},
volume = 152,
year = 2003
}