Rupture processes of the 1999 August 17 Izmit and November 12 Düzce (Turkey) earthquakes

The magnetotelluric (MT) method has been applied to show resistivity variations in the vicinity of the epicenter of the 1999 Düzce earthquake (M w = 7.2) where a large rupture velocity difference was seen between the western and eastern parts of the epicenter. MT data for frequencies ranging between 320 and 0.0005 Hz were acquired along two parallel profiles to the west and the east of Düzce earthquake's epicenter. Both profiles crossed the Düzce basin and the Düzce fault in the north and the North Anatolian Fault (NAF) in the south. MT data analysis shows almost two-dimensionality in the region, at the depth starting from 2-3 km beneath the surface. According to two-dimensional MT modeling, a higher resistive layer extends beneath the eastern side of Düzce earthquake epicenter, compared with the western side. This resistivity structure correlates well with the aftershock distribution of the Düzce earthquake.

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“…On the other hand, Tibi et al (2001) obtained the Düzce fault strike from teleseismic body waves as N75…”

Section: Discussionmentioning

confidence: 99%

Asperity along the North Anatolian Fault imaged by magnetotellurics at Düzce, Turkey

et al. 2009

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“…Tibi et al, 2001;Barka et al, 2002;Aktar et al, 2004) rupturing an almost 200 km long segment (see Fig. 1b).…”

Section: Tectonic Settingmentioning

confidence: 89%

“…The Izmit event occurred on 17 August 1999 and analyses of surface rupture, teleseismic, strong motion and geodetic data all indicate a separation of the mainshock into subevents occurring on distinct fault segments (e.g. Reilinger et al, 2000;Tibi et al, 2001;Barka et al, 2002;Delouis et al, 2002). The western termination of the Izmit rupture is located offshore beneath the Sea of Marmara SE of the Prince Islands in direct vicinity to the Istanbul Metropolitan region Özalaybey et al, 2002).…”

Section: Tectonic Settingmentioning

confidence: 99%

Seismotectonic setting at the North Anatolian Fault Zone after the 1999 Mw=7.4 Izmit earthquake based on high-resolution aftershock locations

et al. 2008

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Abstract. The most recent devastating earthquakes that occurred along the North Anatolian Fault Zone (NAFZ) in northwestern Turkey were the 1999 Izmit (Mw=7.4) and Düzce (Mw=7.1) events. In this study we present a catalog of Izmit aftershock hypocenters that was deduced from a network covering the entire 140 km long rupture of the mainshock. 7348 events with a location accuracy better than 5 km are analysed. Aftershocks were observed along the entire ruptured segment along a 20 km wide band of activity. Events are clustered in distinct regions and dominantly occur at 5 to 15 km depth. The eastern termination of the Izmit rupture is characterized by a sharp and steeply dipping boundary exactly where the Düzce mainshock initiated 87 days after the Izmit event. Relocation of the events using double-difference technology results in 4696 high-resolution hypocenters that allow resolving the internal structure of the seismically active areas with a resolution of 300 m (horizontal) and 400m (vertical). Below the Akyazi Plain, representing a small pull-apart structure at a triple junction of the NAFZ, we identify planes of activity that can be correlated with nodal planes of EW extensional normal faulting aftershocks. Along the easternmost Karadere-Düzce segment we identify the down-dip extension of the Karadere fault that hosted about 1 m of right-lateral coseismic slip. At the easternmost rupture we correlate a cloud-type distribution of seismic activity with the largest aftershocks in this area, a subevent of the Izmit mainshock and the Düzce mainshock that all have an almost identical focal mechanism. This part of the NAFZ is interpreted as a classical example of a seismic barrier along the fault.

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“…This series then systematically propagated westward toward the Istanbul-Marmara area (Stein et al, 1997). The most recent events occurred near İzmit and Düzce in 1999, which suffered M w 7.4 and 7.1 earthquakes, respectively (Tibi et al, 2001;Barka et al, 2002).…”

Section: Tectonic Setting and The Gonaf Projectmentioning

confidence: 97%

Seismic‐Wave Propagation in Shallow Layers at the GONAF‐Tuzla Site, Istanbul, Turkey

Raub

Bohnhoff

Petrović

et al. 2016

Bulletin of the Seismological Society of America

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Using the first dataset available from the downhole Geophysical Observatory of the North Anatolian Fault, we investigated near-surface seismic-wave propagation on the Tuzla Peninsula, Istanbul, Turkey. We selected a dataset of 26 seismograms recorded at Tuzla at sensor depths of 0, 71, 144, 215, and 288 m. To determine near-surface velocities and attenuation structures, the waveforms from all sensors were pairwise deconvolved and stacked. This produced low-noise empirical Green's functions for each borehole depth interval. From the Green's functions, we identified reflections from the free surface and a low-velocity layer between ∼90 and ∼140 m depth. The presence of a low-velocity zone was also confirmed by a sonic log run in the borehole. This structure, plus high near-surface P-and S-wave velocities of ∼3600-4100 and ∼1800 m=s, lead to complex interference effects between upgoing and downgoing waves. As a result, the determination of quality factors (Q) with standard spectral ratio techniques was not possible. Instead, we forward modeled the Green's functions in the time domain to determine effective Q values and to refine our velocity estimates. The effective Q P values for the depth intervals of 0-71, 0-144, 0-215, and 0-288 m were found to be 19, 35, 39, and 42, respectively. For the S waves, we obtained an effective Q S of 20 in the depth interval of 0-288 m. Considering the assumptions made in our modeling approach, it is evident that these effective quality factors are biased by impedance contrasts between our observation points. Our results show that, even after correcting for a free-surface factor of 2, the motion at the surface was found to be 1.7 times greater than that at 71 m depth. Our efforts also illustrate some of the difficulties of dealing with site effects in a strongly heterogeneous subsurface.Online Material: Plots of resistivity and caliper logs and the spectra of all 26 events.

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Rupture processes of the 1999 August 17 Izmit and November 12 Düzce (Turkey) earthquakes

Cited by 92 publications

References 11 publications

Asperity along the North Anatolian Fault imaged by magnetotellurics at Düzce, Turkey

Asperity along the North Anatolian Fault imaged by magnetotellurics at Düzce, Turkey

Seismotectonic setting at the North Anatolian Fault Zone after the 1999 Mw=7.4 Izmit earthquake based on high-resolution aftershock locations

Seismic‐Wave Propagation in Shallow Layers at the GONAF‐Tuzla Site, Istanbul, Turkey

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