The seismic velocity and fault structure of the Erzincan basin, Turkey, using local earthquake tomography

Abstract

S U M M A R YWe present a detailed 3-D seismic velocity model for the upper crust, beneath the Erzincan Basin using tomographic inversion applied to the bodywave arrivals of the 1992 March 13 Erzincan earthquake (M l = 6.9) aftershock sequence. High quality digital data collected by various institutions is used, consisting of 1240 hypocentres with rms errors less than 0.10 s, recorded by 25 stations on average. This provides a total of approximately 21 000 P-and 10 000 S-arrival times. The final solution is well constrained and reveals sharp boundaries bordering the basin. The shape of the basin is found to be deeper on the north and narrower at the eastern border. The velocity contrast related to the basin extends down to a depth of 3 km, but is hardly perceptible at 6 km and completely disappears at 9 km. The thickness of low-velocity unconsolidated soft sediments (V p < 2000 m s −1 ) is estimated to be shallower than 3 km. The hypocentres were relocated using the inferred 3-D model and correlated with the fault segments that were observed in field studies. In addition to the main segment of the North Anatolian Fault (NAF), on the north of the basin, we identified a secondary faulted zone located along the southern border of the basin and merging with the Pulumur Fault Zone. We observed that this southern zone has a limited extension towards east (∼20 km) and therefore played only a minor role in the evolution of the basin. Despite the complex interaction between the North Anatolian Fault, the Ovacık Fault and the Pulumur Fault Zone, it is clear that the Erzincan Basin has developed predominantly by the pull-apart mechanism. We conclude that the main continuation of NAF to the east is the branch on the north following the Euphrates valley, and constitutes, locally, the primary seismic hazard factor.

Distribution of Seismic Velocities and Attenuation in the Crust beneath the North Anatolian Fault (Turkey) from Local Earthquake Tomography

“…The crustal seismic structure in the western part of the NAFZ has been the focus of several tomographic studies performed by different research groups (e.g., Nakamura et al, 2002;Aktar et al, 2004;Baris et al, 2005;Salah et al, 2007). Most of them were based on the inversion of P-and S-wave travel-time arrivals from local seismicity recorded by stations belonging to temporary and/or permanent networks.…”

Direct Empirical Estimation of Arrival-Time Picking Error from Waveform Cross-Correlations

“…But the variance of the sum (or difference) of two uncorrelated, random, normal variables is simply the sum of the variances, so σ 2 dt p dt x 2σ 2 p : Thurber (1983) Coyote Lake, California 0.14 (P) local Eberhart-Phillips (1990) Coalinga, California 0.12 (P, S) local Cardaci et al (1993) Etna volcano, Italy 0.0095 (P, S) local Foxall et al (1993) Santa Cruz Mountains, California 0.092 (P) local Ligdas and Lees (1993) Northern Greece 0.08 (P, S) local Zhao and Kanamori (1993) Landers, California 0.16 (P) local Scott et al (1994) San Jacinto fault, California 0.023 (P) local Dorbath and Granet (1996) Altiplano and Cordillera, Bolivia 0.26 (P); 0.54 (S) near-regional Pujol (1996) Northridge, California 0.11 (P, S) local Symons and Crosson (1997) Puget Sound, Washington 0.14 (P) local Bounif and Dorbath (1998) Constantine, Algeria 0.11 (P, S) local Alessandrini et al (2001) Central Appennines, Italy 0.08 (P); 0.14 (S) local Jones et al (2001) Mount Pinatubo, Philippines 0.025 (P) local Drakatos et al (2002) Central Greece 0.30 (P, S) near-regional van Wagoner et al (2002) Puget Sound, Washington 0.097 (P) local Baher and Davis (2003) Northridge, California 0.105 (P) local Husen et al (2003) Costa Rica 0.25 (P) near-regional Mukhopadhyay and Kayal (2003) Chamoli, India 0.46 (P, S) near-regional Sherburn et al (2003) Taupo volcano, New Zealand 0.06 (P, S) local Zhang and Thurber (2003) Hayward fault, California 0.024 (P, S) local Aktar et al (2004) Erzincan Basin, Turkey 0.12 (P) local Eberhart-Phillips and Michael (2004) Loma Prieta, California 0.118 (P) local Huang and Zhao (2004) Beijing, China 0.402 (P, S) near-regional Landes et al (2004) Vrancea, Romania 0.38 (P) near-regional Molina et al (2005) Tungurahua volcano, Ecuador 0.065 (P) local Shibutani and Katao (2005) Tottori, Japan 0.042 (P, S) local Bannister et al (2006) Arthur's Pass, New Zealand 0.037 (P, S) local Gautier et al (2006) Gulf of Corinth, Greece 0.106 (P, S) local Monteiller et al (2006) Kiluaea volcano 0.07 (P) local …”

Three‐dimensional VP and VP/VS structure of the upper crust in the Erzincan basin (eastern Turkey)

“… Gaucher [1994], using the delays with respect to first arrivals of converted phases SP for some aftershocks of the 1992 Erzincan earthquake, estimated the basin depth as between 0.65 and 2.1 km in the southeastern part of the basin. Recently, Aktar et al [2004] estimated the thickness of the low‐velocity unconsolidated soft sediments ( V P < 2 km/s) to be shallower than 3 km.…”

“…Until a few recent studies [ Aktar et al 2004; Kaypak and Eyidoğan , 2005], the deep seismic velocity structure of the Erzincan basin was poorly known. A simple crustal velocity model for the basin was obtained by Cisternas et al [1992] for locating the aftershocks of the 1992 Erzincan earthquake.…”