The distribution of plate motion between multiple fault strands and how this distribution may evolve remain poorly understood, despite the key implications for seismic hazards. The North Anatolian Fault in northwest Turkey is a prime example of a multistranded continental transform. Here we present the first constraints on late Quaternary slip rates on its northern branch across the Cinarcik Basin in the eastern Marmara Sea. We use both deep penetration and high‐resolution multichannel seismic reflection data with a stratigraphic age model to show that a depocenter has persisted near the fault bend responsible for that transform basin. Successively older depocenters have been transported westward by fault motion relative to Eurasia, indicating a uniform right‐lateral slip rate of 18.5 mm/yr over the last 500,000 years, compared to overall GPS rates (23–24 mm/yr). Thus, the northern branch has slipped at a nearly constant rate and has accounted for most of the relative plate motion between Eurasia and Anatolia since ~0.5 Ma.
A regional west striking system of surface and blind faults transects northern metropolitan Los Angeles, separating the Santa Monica Mountains from two deep sedimentary basins. The surface faults include the Santa Monica, Dume, and Malibu Coast faults. The three‐dimensional (3‐D) geometries of these faults and deformed dated strata were examined in order to determine how oblique shortening is accommodated, how structural relief grows along a mountain front, and how block translation is related to block rotation. Industry seismic reflection, well, and outcrop data were used to construct digital structure‐contour maps of several of these faults and three stratigraphic horizons that intersect them. These maps, swath bathymetry, digital elevation models, and seismicity were incorporated into a 3‐D digital database. Modeling included new approaches to determining strike‐slip displacement by separate analyses of shortening and structural relief in a restraining double bend. Stratigraphic thicknesses indicate Miocene extension across the Santa Monica and Dume faults, which have been reactivated as a single or linked moderately dipping arcuate fault that accommodates one coherent block motion via left‐lateral and left‐reverse displacement. Modeling indicates 5 km (+8/−1 km) of left‐lateral displacement on part of the Santa Monica–Dume fault and ∼11° of clockwise rotation of the Santa Monica Mountains during the last ∼4 ± 1 m.y. Modern displacement rates modeled from GPS data are similar to our modeled post‐∼4 Ma rates of westward escape and clockwise rotation of the Santa Monica Mountains.
A rigid element method of restoration (UNFOLD) is used to restore competent folded and faulted layers of the Ventura and Los Angeles basins to their initial horizontal state. Comparison of initial (undeformed) state with present (deformed state) allows one to estimate both the finite crustal deformation and its associated horizontal displacement field (relative to an arbitrary fixed line). Including data from the Santa Barbara Channel basin, the total finite displacement field for the western Transverse Ranges and vicinity (within the Pacific plate) is inferred from this map restoration and is modeled as a double fan closure. This model implies a 10° clockwise rotation of the northern boundary of the western Transverse Ranges and a 5° counterclockwise rotation of its northeast boundary. Lateral variation of the deformation reveals the heterogeneity of the subsurface deformation. Most of the major thrusts appear to initiate as en echelon structures along the left‐lateral northern margin and the right‐lateral northeastern margin of the studied area. The resulting deformation and displacement values closely match those derived by other geological methods (section balancing techniques or fault slip measurements) and by geophysical methods (geodetic, paleomagnetic, and focal mechanism data). Map restoration thus is a method that can independently quantify both local and regional deformation including folds and faults. This method also reveals the zones where problems of compatibility appear with the available geological and geophysical data and thus where the next studies might be focused.
