Slip distribution and stress changes associated with the 1999 November 12, Duzce (Turkey) earthquake (M (w)=7.1)

The 1999 November 12 Duzce earthquake (M (w) = 7.1) was apparently the eastward extension of the August 17, Izmit earthquake (M (w) = 7.4). The Duzce event caused heavy damage and fatalities in the cities of Duzce and Bolu. Here a finite-fault inversion method with five discrete time windows is applied to derive the co-seismic slip distribution of the Duzce earthquake. The fault plane is best modelled as a 40 x 20 km(2) plane, with a strike of 262degrees and a dip of 65degrees to the north, and that the majority of slip occurred in two distinct patches on either side of the hypocentre, implying bilateral rupture. The possible triggering of this event by the Izmit earthquake is investigated using Coulomb stress modelling of all large events since 1943 with the inclusion of secular loading. The results show that although the Duzce rupture plane was in a stress shadow prior to the Izmit earthquake, that event caused a significant Coulomb stress load, taking the Duzce fault out of the stress shadow, which probably precipitated failure. A comparison of the mapped Coulomb stress change with the inferred slip shows no correlation between the two. Finally, the stress modelling indicates that the northern branch of the North Anatolian fault zone, beneath the Sea of Marmara towards the city of Istanbul, is presently the most highly loaded segment of the North Anatolian Fault Zone

New constraints on micro-seismicity and stress state in the western part of the North Anatolian Fault Zone : Observations from a dense seismic array

Major funding was provided by the UK Natural Environment Research Council (NERC) under grant NE/I028017/1 and partially supported by Boğaziçi University Research Fund (BAP) under grant 6922. We would like to thank all the project members from the University of Leeds, Boğaziçi University, Kandilli Observatory, Aberdeen University and Sakarya University. I would also like to thank Prof. Ali Pinar and Dr. Kıvanç Kekovalı for their valuable comments. Some of the figures were generated by GMT software (Wessel and Smith, 1995).Peer reviewedPostprin

Structure of the northwestern North Anatolian Fault Zone imaged via teleseismic scattering tomography

Information on fault zone structure is essential for our understanding of earthquake mechanics, continental deformation and seismic hazard. We use the scattered seismic wavefield to study the subsurface structure of the North Anatolian Fault Zone (NAFZ) in the region of the 1999 İzmit and Düzce ruptures using data from an 18-month dense deployment of seismometers with a nominal station spacing of 7 km. Using the forward- and back-scattered energy that follows the direct P-wave arrival from teleseismic earthquakes, we apply a scattered wave inversion approach and are able to resolve changes in lithospheric structure on a scale of 10 km or less in an area of about 130 km by 100 km across the NAFZ. We find several crustal interfaces that are laterally incoherent beneath the surface strands of the NAFZ and evidence for contrasting crustal structures either side of the NAFZ, consistent with the presence of juxtaposed crustal blocks and ancient suture zones. Although the two strands of the NAFZ in the study region strike roughly east–west, we detect strong variations in structure both north–south, across boundaries of the major blocks, and east–west, parallel to the strike of the NAFZ. The surface expression of the two strands of the NAFZ is coincident with changes on main interfaces and interface terminations throughout the crust and into the upper mantle in the tomographic sections. We show that a dense passive network of seismometers is able to capture information from the scattered seismic wavefield and, using a tomographic approach, to resolve the fine scale structure of crust and lithospheric mantle even in geologically complex regions. Our results show that major shear zones exist beneath the NAFZ throughout the crust and into the lithospheric mantle, suggesting a strong coupling of strain at these depths

Monitoraggio in area sismica di beni monumentali: tecniche NDT e procedure di verifica

Negli ultimi anni il concetto di vulnerabilità sismica è tristemente entrato a far parte delle conoscenze anche dei non addetti ai lavori. Infatti, gli eventi sismici che hanno interessato dagli inizi del ‘900 il territorio Italiano, hanno sistematicamente messo in risalto l’elevata vulnerabilità sismica del nostro patrimonio edilizio, ivi compresi i beni monumentali, nonché, l’inesistenza di qualsiasi attività di programmazione della manutenzione periodica ordinaria e straordinaria delle strutture sismo-resistenti, che garantiscono nel tempo la conservazione delle loro capacità di risposta alle perturbazioni esterne.Il progetto PON sul Monitoraggio in Area Sismica di SIstemi MOnumentali nasce con la prerogativa di produrre uno strumento dedicato alla tutela di strutture a valenza storico – artistica, attraverso un percorso di catalogazione, di analisi del bene inteso come elemento costituito da elementi resistenti e da materiali, di studio del sito dove la struttura è ubicata e di attività di monitoraggio

Equations for the estimation of strong ground motions from shallow crustal earthquakes using data from Europe and the Middle East : vertical peak ground acceleration and spectral acceleration

This article presents equations for the estimation of vertical strong ground motions caused by shallow crustal earthquakes with magnitudes M w 5 and distance to the surface projection of the fault less than 100km. These equations were derived by weighted regression analysis, used to remove observed magnitude-dependent variance, on a set of 595 strong-motion records recorded in Europe and the Middle East. Coefficients are included to model the effect of local site effects and faulting mechanism on the observed ground motions. The equations include coefficients to model the observed magnitude-dependent decay rate. The main findings of this study are that: short-period ground motions from small and moderate magnitude earthquakes decay faster than the commonly assumed 1/r, the average effect of differing faulting mechanisms is similar to that observed for horizontal motions and is not large and corresponds to factors between 0.7 (normal and odd) and 1.4 (thrust) with respect to strike-slip motions and that the average long-period amplification caused by soft soil deposits is about 2.1 over those on rock sites

A detailed source study of the Orta (Cankiri) earthquake of June 6, 2000 (M-S=6.1): An intraplate earthquake in central Anatolia

The devastating. Izmit and Duzce earthquakes were followed by the Orta intra-plate earthquake (M-S = 6.1) occurred in the central Anatolian block on June 6, 2000. The focal mechanism, aftershock distribution and the field studies (Emre et al., 2000) suggest a movement on a 21-km long Dodurga fault striking nearly N-S where the sense of motion is left-lateral strike-slip with considerable amount of normal component. We applied the constrained linear finite-fault inversion method of Hartzell and Heaton (1983) to the teleseismic P and SH waveforms to derive a coseismic slip distribution model for the earthquake. Time windows approach is applied allowing variable rise times and rupture velocities. The source-rise time function is discretized into consecutive time intervals that stand for slip contribution of individual subfaults. Although no clear surface ruptures were associated with the earthquake, the resulting slip model suggests coseismic slip in the order of several tens of centimetres. Our coseismic slip distribution model identifies two slip patches with the following maximum slip values: (1) the larger one (42 cm) is located to the south of the hypocenter at depth range of 4-8 km and (2) the smaller one (31 cm) is located just above and north of the hypocenter. The slip-model yield a seismic moment of 1.0 x 10(18) Nm, most of which is released from the rupture over the depth of 8 km

A detailed slip model for the 1995, October 1, Dinar, Turkey, earthquake (M-S=6.1) determined from inversion of teleseismic P and SH waveforms

Teleseismically recorded P and SH waveforms of the 1995, October 1 Dinar, Turkey, earthquake are inverted to find detailed coseismic slip distribution on the ruptured part of the Dinar-Civril fault. For this purpose a linear finite-fault inversion procedure with time window approach is used to allow variable rise time and rupture velocity on the model fault. The source is represented by a 24 x 21 km rectangle fault plane, which is divided into 56 equal size subfaults. The strike and the dip of the fault plane are assumed as determined by a previous study. The amount of slip and the rake angle on each subfault is retrieved through fitting the observed and synthetic seismograms in a least-squares sense. The previous inversion studies indicated that the earthquake was associated with two subevents, with a 6 stime lag of the NW subevent. Therefore, the model fault plane is also divided into two separate equal-area segments, the SE and the NW segments, to delay the rupture propagation over the NW segment. We tried several models to fix the delay time and hypocentral depth and to explain the waveforms. The smallest misfit error resulted from a model with 5 s delay time and 7.5 km hypocentral depth. The preferred solution suggests that the earthquake is associated with breaking of two asperities and the coseismic slip occurred mostly above the depth of 10 km. The smaller asperity is located to the SE just beneath Dinar town with peak slip of 26 cm while the larger one is located to the NW with peak slip of 41 cm. The observed surface rupture coincides with the location of the smaller asperity. The seismic moment for our slip model is 2 8 x 10(18) N m. The modelling yields an average rake angle of -102degrees and almost no difference between the average rake angles of the two asperities