From 1998 to 2000, we have studied the evidence for large paleoearthquakes at the Rurrand Fault. This fault represents the eastern border of the Roer Valley Graben, which is the tectonically most active region in the Lower Rhine Embayment. The purpose of our paleoseismological studies is to enlarge the seismicity data base for this region beyond instrumental records and historical reports using indications of surface-faulting events from stratigraphie conditions at active faults. Larger time spans considered in the earthquake catalogue will enable a more reliable statistical analysis which is required for seismic hazard assessment. Based on analyses of geological data and géomorphologie investigations, detailed geophysical surveying was carried out along the southern Rurrand Fault segment for the selection of a site appropriate to paleoseismological studies. Mapping of physical parameter contrasts with seismic reflection, VES, ERT, and GPR measurements along fault-crossing profiles inferred position and near-surface structure of the fault. At the site promising the best conditions, a trench was excavated across the fault near the city of Jiilich, Germany. Within a depth of about 4 m, the Rurrand Fault was exposed in an about 50 m-wide system of faults and fault zones, affecting the stratigraphie sequence with various displacement characteristics and amounts of throw. According to heavy mineral analyses, the deposition time of most the exposed sediment strata was assigned to Pliocene and Lower Pleistocene time. These geological units are covered by loess layers deposited through so-lifluction processes during the Weichselian glacial, i.e. some tens of ka B.P., or – with lower probability – during the Saalian glacial. Several faults which had also affected the loess reflect younger fault activity. However, clear paleoseismic features were not observed in the trench, thus an unambiguous proof of the occurrence of coseismic fault displacements could not be furnished. Recently, differential subsidence due to drainage takes place in the surroundings of the nearby opencast mining. An amount of some 0.35 m, concentrated in a very narrow lateral zone, has been observed during the last 40 a at about 1 km distance from the trench position. To date, the subsidence could not be clearly located in the trench exposure. Results from geodetic levelling campaigns will help to determine the offset residuals and to gain better insight into the ruling displacement processes at the Rurrand Fault.

Relay ramps form at different scales in extensional terrains to accommodate the differential stretching among the overlapping bounding-normal fault segments. The major boundary structure of the Gediz Graben (SW Turkey) is segmented, with formation, evolution and active breaching of relay ramps. The Akçapınar relay ramp is an example of these processes that forms within a 2 km wide overlap zone between ∼ E–W-trending segments on the southern margin of the Gediz Graben. Change of structural style at the ramp area is clearly evident from variations in the orientation of fractures and faults of the relay ramp. As a site of local stress field anomaly, ∼ N–S-trending structures in the Akçapınar relay ramp are conformable with the extension that is parallel to the bounding faults of the relay ramp. These structures are also superimposed onto the ∼ E–W-trending regional structural style by an obvious cross-cutting relationship, suggesting both spatial and temporal variation of the state of stress at the ramp area during the relay ramp formation. The regional stress field and the resulting regional structural style characterize the earlier stages of ramp evolution, during which segment interaction is limited. As segment interaction and relay ramp formation advances towards the breaching phase, an anomalous local stress field arises and the relay ramp area experiences extension parallel to the bounding normal faults, that is, transverse to the regional direction of extension. This creates a new structural style at the ramp area.

Western Turkey is one of the most spectacular regions of widespread active continental extension in the world. The most prominent structures of this region are E–W-trending grabens (e.g. Gediz and Büyük Menderes grabens) and intervening horsts, exposing the Menderes Massif. This paper documents the result of a recent field campaign (field geological mapping and structural analysis) along the southern margin of the modern Gediz Graben of Pliocene (∼ 5 Ma) age. This work provides field evidence that the presently low-angle ductile-brittle detachment fault is cut and displaced by the high-angle graben-bounding normal faults with total displacement exceeding 2.0 km. The evolution of the N–S extension along the Gediz Graben occurred during two episodes, each characterized by a distinct structural styles: (1) rapid exhumation of Menderes Massif in the footwall of low-angle normal fault (core-complex mode) during the Miocene; (2) late stretching of crust producing E–W grabens along high-angle normal faults (rift mode) during Pliocene–Quaternary times, separated by a short-time gap. The later phase is characterized by the deposition of now nearly horizontal sediments of Pliocene age in the hanging walls of the high-angle normal faults and present-day graben floor sediments. The evolution of extension is at variance with orogenic collapse and/or back-arc extension followed by the combined effect of tectonic escape and subduction rollback processes along the Aegean-Cyprean subduction zone. Consequently, it is misleading to describe the Miocene sediments exhumed on shoulders of the Gediz Graben as simple graben fill.