The Interpretation of Crustal Dynamics Data in Terms of Plate Interactions and Active Tectonics of the Anatolian Plate and Surrounding Regions in the Middle East

During the past 6 months, efforts were concentrated on the following areas: (1) Continued development of realistic, finite element modeling of plate interactions and associated deformation in the Eastern Mediterranean; (2) Neotectonic field investigations of seismic faulting along the active fault systems in Turkey with emphasis on identifying seismic gaps along the North Anatolian fault; and (3) Establishment of a GPS regional monitoring network in the zone of ongoing continental collision in eastern Turkey (supported in part by NSF)

Application of Global Positioning Measurements to Continental Collision in the Pamir-Tien Shan Region, Central Asia and GPS Survey of the Western Tien Shan

In this report, we summarize what we have accomplished with five years of funding from NASA under its DOSE program, and with a comparable level of funding from NSF. We describe the development of a GPS network in the Tien Shan of Kyrgyzstan and Kazakhstan of the former Soviet Union, the analysis of data, and the main results. This discussion presents the state of the current network, which has grown significantly since the termination of our DOSE grants, with continued support both from NSF through its continental dynamics program and from NASA's SENH program. Although grants from NASA's DOSE program did not support this growth not directly, it did so indirectly by building the infrastructure that has enabled further expansion in an area where otherwise there would be only a small GPS presence. We note how the network has grown over time, but the emphasis of this discussion is on the quantity and quality of measurements that we have made

GPS survey of the western Tien Shan

There were two major developments in 1994 in our collaborative GPS experiment in the Tien Shan of the Former Soviet Union (FSU). Both were motivated by our expectation that we will ultimately obtain better science at lower cost if we involve our colleagues in the FSU more deeply in (1) the collection and (2) the analysis of data. As an experimental test of the concept of having our local collaborators carry out the field work semi-autonomously, we sent 6 MIT receivers to the Tien Shan for a period of 3 months. To enable our collaborators to have the capability for data analysis, we provided computers for two data analysis centers and organized a two-week training session. This report emphasizes the rationale for deeper involvement of FSU scientists, describes the training sessions, discusses the data collection, and presents the results. We also discuss future plans. More detailed discussion of background, general scientific objectives, discussions with collaborators, and results for the campaigns in 1992 and 1993 have been given in previous reports

Report of the panel on plate motion and deformation, section 2

Given here is a panel report on the goals and objectives, requirements and recommendations for the investigation of plate motion and deformation. The goals are to refine our knowledge of plate motions, study regional and local deformation, and contribute to the solution of important societal problems. The requirements include basic space-positioning measurements, the use of global and regional data sets obtained with space-based techniques, topographic and geoid data to help characterize the internal processes that shape the planet, gravity data to study the density structure at depth and help determine the driving mechanisms for plate tectonics, and satellite images to map lithology, structure and morphology. The most important recommendation of the panel is for the implementation of a world-wide space-geodetic fiducial network to provide a systematic and uniform measure of global strain

Estimates of Seismic Potential in the Marmara Sea Region from Block Models of Secular Deformation Constrained by Global Positioning System Measurements

We model the geodetically observed secular velocity field in northwestern Turkey with a block model that accounts for recoverable elastic-strain accumulation. The block model allows us to estimate internally consistent fault slip rates and locking depths. The northern strand of the North Anatolian fault zone (NAFZ) carries approximately four times as much right-lateral motion (∼24 mm/yr) as does the southern strand. In the Marmara Sea region, the data show strain accumulation to be highly localized. We find that a straight fault geometry with a shallow locking depth of 6-7 km fits the observed Global Positioning System velocities better than does a stepped fault geometry that follows the northern and eastern edges of the sea. This shallow locking depth suggests that the moment release associated with an earthquake on these faults should be smaller, by a factor of 2.3, than previously inferred assuming a locking depth of 15 km.Earth and Planetary Science

Izmit earthquake postseismic deformation and dynamics of the North Anatolian Fault Zone

We have modeled postseismic deformation from 1999 to 2003 in the region surrounding the 1999 Izmit and Diizce earthquake ruptures, using a three-dimensional viscoelastic finite element method. Our models confirm earlier findings that surface deformation within the first few months of the Izmit earthquake is principally due to stable frictional afterslip on and below the Izmit earthquake rupture. A second deformation process is required, however, to fit the surface deformation after several months. Viscoelastic relaxation of lower crust and/or upper mantle with a viscosity of the order of 2 to 5 x 1019 Pa s improves the models' fit to later GPS site velocities. However, for a linear viscous rheology, this range of values is inconsistent with highly localized interseismic deformation around the North Anatolian Fault Zone (NAFZ) that was well observed prior to the earthquake sequence. The simplest solution to this problem is to assume that the effective viscosity of the relaxing material increases with time after large earthquakes, that is, that it has a power law or Burger's body (transient) rheology. A Burger's body rheology with two characteristic viscosities (2 to 5 x 1019 Pa s and at least 2 x 1020 Pa s) in the mantle is consistent with deformation around the NAFZ throughout the earthquake cycle

Seven years of postseismic deformation following the 1999, M = 7.4 and M = 7.2, Izmit-Duzce, Turkey earthquake sequence

We report the results of nearly 7 years of postseismic deformation measurements using continuously recorded and survey mode GPS observations for the 1999 Izmit-Düzce earthquake sequence. Resolvable, time-dependent postseismic changes to the preearthquak

Postseismic deformation following the 1991 Racha, Georgia earthquake

The 1991, Ms = 7.0 Racha earthquake is the largest ever recorded in the Caucasus Mountains. Approximately three months after this thrust-faulting earthquake, a GPS network was set up to measure postseismic surface deformation. We present an analysis of these data, which indicate accelerated postseismic motions at several nearfield sites. We model this deformation as either afterslip on the rupture surface or viscoelastic relaxation of the lower crust. We find that the postseismic motions are best explained by shallow afterslip on the earthquake rupture plane. The minimum postseismic moment release is estimated at 6.0 × 1018 N m, which is over 200 times the moment released by aftershocks in this same period and about 20% of the coseismic moment. We also show that the effective viscosity of the lower crust in the western Greater Caucasus region exceeds 1018 Pa s

Seven years of postseismic deformation following the 1999, M = 7.4 and M = 7.2, Izmit-Düzce, Turkey earthquake sequence

We report the results of nearly 7 years of postseismic deformation measurements using continuously recorded and survey mode GPS observations for the 1999 Izmit-Düzce earthquake sequence. Resolvable, time-dependent postseismic changes to the preearthquake interseismic velocity field extend at least as far as the continuous GPS station in Ankara, ∼200 km southeast of the Izmit rupture. Seven years after the earthquake sequence, the relative postseismic velocity across the North Anatolian Fault (NAF) reaches ∼10–12 mm/a, roughly 50% of the steady state interseismic rate, with the highest postseismic velocities within 40 km of the coseismic ruptures. We use a sequence of logarithmic time functions to fit GPS site motions. Up to three logarithmic terms with decay constants of 1, 150, and 3500 days are necessary to fit all the transient motion observed at the continuous GPS stations. The first term is required for the component of site motion parallel to the NAF at near-field sites strongly implicating rapid, shallow afterslip. The intermediate and longer-term postseismic velocity components reflect more broadly distributed strain with a symmetric double-couple pattern suggestive of either localized, deep afterslip or viscoelastic relaxation of the upper mantle and/or lower crust. In two areas (including the Marmara Sea) this pattern is superimposed on north-south extension centered on the NAF. We speculate that this extension may result from aseismic dip slip along coseismically weakened faults, driven by the background tectonic stress.Scientific and Technological Research Council of Turkey (CAYADAG Project 103Y100, EU 6)European Training Foundation (Frame FORESIGHT Project contract 511139)Scientific and Technological Research Council of Turkey (TARAL 1007 Project 105G019)National Science Foundation (U.S.) (grant EAR-0337497)National Science Foundation (U.S.) (grant EAR-0305480)National Science Foundation (U.S.) (grant INT-0001583)Natural Sciences and Engineering Research Council of Canada (Discovery grant RGPIN 261 458-07