Evidence for a bimaterial interface along the Mudurnu segment of the North Anatolian Fault Zone from polarization analysis of P waves

Bulut, Fatih; Ben‐Zion, Yehuda; Bohnhoff, Marco

doi:10.1016/j.epsl.2012.02.001

Cited by 53 publications

(65 citation statements)

References 38 publications

(43 reference statements)

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“…(Biryol et al [2011]). Clear signatures of the presence of the NNAF in the upper crust in this region can also be found in other studies, for example, Bulut et al [2012] find a 6 % change in the velocity of fault head waves across the northern branch of the fault, which is similar to the 3-4 % change in velocity according to our P and S wave velocity models (particularly bearing in mind that the magnitude of the perturbations might be underestimated in the tomography) and a reduction (of 0.2 to 0.6 km/s) in absolute P wave velocity beneath the fault (Behyan and Alkan [2015]). …”

Section: Nnafsupporting

confidence: 62%

“…1) revealed additional information on the structure of its two strands. The presence of different lithologies bounding the northern branch of the NAFZ has been inferred by Bulut et al [2012] and Najdahmadi et al [2016] by tracking fault head waves caused by the presence of a bimaterial interface. This is also consistent with a change in Moho signature and depth observed in the Istanbul Zone and has been attributed to either the presence of a thicker crust (Frederiksen et al [2015]) or a weak Moho underlain by a highly anisotropic layer [2015]).…”

Section: Introductionmentioning

confidence: 99%

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Constraints on North Anatolian Fault zone width in the crust and upper mantle from S-wave teleseismic tomography

Papaleo¹,

Cornwell²,

Rawlinson³

2018

Preprint

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Abstract.We present high resolution S-wave teleseismic tomography images of the western segment of the North Anatolian Fault (NAFZ) in Turkey using teleseismic data recorded during the deployment period of the DANA array. The array comprised 66 stations with a nominal station spacing of 7 km, thus permitting a horizontal and vertical resolution of approximately 15 km. We use the current S-wave results with previously published P-wave teleseismic tomography to produce maps of relative V P /V S anomalies, which we use to highlight the difference in overall composition of the three terranes separated by the northern (NNAF) and southern (SNAF) branches of the NAFZ. Our results show a narrow S-wave low velocity anomaly beneath the northern branch of the NAFZ extending from the upper crust, where it has a width of ∼10 km, to the lower crust, where it widens to ∼30 km. This low velocity zone most likely extends into the upper mantle, where we constrain its width to be ≤50 km and interpret it as indicative of localised shear beneath the NNAF; this structure is similar to what has been observed for the NAFZ west of 32• and therefore we propose that the structure of the NNAF is similar to that of the NAFZ in the east. The SNAF does not show a very strong signature in our images and we conclude that it is most likely rooted in the crust, possibly accommodating deformation related to rotation of the Armutlu/Almacik Blocks situated between the two NAFZ branches. Keypoints:• An ∼15-km resolution teleseismic S-wave velocity model constrains width and depth of the North Anatolian Fault in the crust and upper mantle

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Section: Nnafsupporting

confidence: 62%

Section: Introductionmentioning

confidence: 99%

Constraints on North Anatolian Fault zone width in the crust and upper mantle from S-wave teleseismic tomography

Papaleo¹,

Cornwell²,

Rawlinson³

2018

Preprint

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“…Ideally, the largest eigenvalue of a window containing a FZHW will be larger than noise, and the largest eigenvalue corresponding to a direct P wave would be larger still (Bulut et al 2012;Allam et al 2014b). Eigenvalues are computed for phases generated by the 24 events and recorded at station BB07.…”

Section: Resultsmentioning

confidence: 99%

“…Allam et al 2014b;Najdahmadi et al 2016), we examine HPM in displacement seismograms with consecutive moving time windows of length 0.1 s (20 samples) that overlap by 1 sample. For each window, all three components of motion are combined in a 20×3 matrix, the covariance of the matrix is computed (Bulut et al 2012) and the largest eigenvalue and eigenvector of the covariance matrix (major axis of the polarization ellipse) are obtained. We then test to see if the azimuth of the largest eigenvector for windows starting at the FZHW and direct P picks point, respectively, towards the fault and the epicentre direction.…”

Section: Resultsmentioning

confidence: 99%

“…For events with focal mechanisms coinciding with the fault, FZHW and trailing direct P waves have opposite first motion polarities (BenZion & Malin 1991;Ross & Ben-Zion 2014). Also, FZHW are radiated from the fault and have horizontal particle motion (HPM) with a significant fault-normal component (Bulut et al 2012;Allam et al 2014b;. In contrast, HPM of direct P waves points in the epicentre direction.…”

Section: Methodsmentioning

confidence: 99%

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Internal structure of the San Jacinto fault zone at Blackburn Saddle from seismic data of a linear array

Ben‐Zion

Ross

et al. 2017

Geophysical Journal International

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S U M M A R YLocal and teleseismic earthquake waveforms recorded by a 180-m-long linear array (BB) with seven seismometers crossing the Clark fault of the San Jacinto fault zone northwest of Anza are used to image a deep bimaterial interface and core damage structure of the fault. Delay times of P waves across the array indicate an increase in slowness from the southwest most (BB01) to the northeast most (BB07) station. Automatic algorithms combined with visual inspection and additional analyses are used to identify local events generating fault zone head and trapped waves. The observed fault zone head waves imply that the Clark fault in the area is a sharp bimaterial interface, with lower seismic velocity on the southwest side. The moveout between the head and direct P arrivals for events within ∼40 km epicentral distance indicates an average velocity contrast across the fault over that section and the top 20 km of 3.2 per cent. A constant moveout for events beyond ∼40 km to the southeast is due to off-fault locations of these events or because the imaged deep bimaterial interface is discontinuous or ends at that distance. The lack of head waves from events beyond ∼20 km to the northwest is associated with structural complexity near the Hemet stepover. Events located in a broad region generate fault zone trapped waves at stations BB04-BB07. Waveform inversions indicate that the most likely parameters of the trapping structure are width of ∼200 m, S velocity reduction of 30-40 per cent with respect to the bounding blocks, Q value of 10-20 and depth of ∼3.5 km. The trapping structure and zone with largest slowness are on the northeast side of the fault. The observed sense of velocity contrast and asymmetric damage across the fault suggest preferred rupture direction of earthquakes to the northwest. This inference is consistent with results of other geological and seismological studies.

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Fault Zone Guided Wave generation on the locked, late interseismic Alpine Fault, New Zealand

Eccles

Gulley

Malin

et al. 2015

Geophysical Research Letters

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Fault Zone Guided Waves (FZGWs) have been observed for the first time within New Zealand's transpressional continental plate boundary, the Alpine Fault, which is late in its typical seismic cycle. Ongoing study of these phases provides the opportunity to monitor interseismic conditions in the fault zone. Distinctive dispersive seismic codas (~7–35 Hz) have been recorded on shallow borehole seismometers installed within 20 m of the principal slip zone. Near the central Alpine Fault, known for low background seismicity, FZGW‐generating microseismic events are located beyond the catchment‐scale partitioning of the fault indicating lateral connectivity of the low‐velocity zone immediately below the near‐surface segmentation. Initial modeling of the low‐velocity zone indicates a waveguide width of 60–200 m with a 10–40% reduction in S wave velocity, similar to that inferred for the fault core of other mature plate boundary faults such as the San Andreas and North Anatolian Faults.

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Evidence for a bimaterial interface along the Mudurnu segment of the North Anatolian Fault Zone from polarization analysis of P waves

Cited by 53 publications

References 38 publications

Constraints on North Anatolian Fault zone width in the crust and upper mantle from S-wave teleseismic tomography

Constraints on North Anatolian Fault zone width in the crust and upper mantle from S-wave teleseismic tomography

Internal structure of the San Jacinto fault zone at Blackburn Saddle from seismic data of a linear array

Fault Zone Guided Wave generation on the locked, late interseismic Alpine Fault, New Zealand

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