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1.
David Verdonck   《Tectonophysics》2006,417(3-4):221-230
Data from 29 tide gauges and 113 pairs of first and second order leveling lines are analyzed to determine the pattern of vertical deformation in the Pacific Northwest of the United States. The data span nearly 100 years and represent the interseismic elastic deformation related to the great earthquake cycle. Uplift rates calculated from leveling surveys are adjusted to a model surface in the tidal reference frame using a robust, weighted, linear, least square technique. Rapid uplift occurs in two distinct broad regions along the coast separated by a narrow zone of slow subsidence. Vertical deformation rates range from > 4 mm/year of uplift on southern Vancouver Island to > 2 mm/year of subsidence in northern coastal Oregon. The deformation pattern is consistent with the results of previous studies and subduction models.  相似文献   

2.
A. Demoulin  E. Hallot 《Tectonophysics》2009,474(3-4):696-708
A good evaluation of the Quaternary uplift of the Rhenish shield is a key element for the understanding of the Cenozoic geodynamics of the western European platform in front of the alpine arc. Previous maps of the massif uplift relied on fluvial incision data since the time of the rivers' Younger Main Terrace to infer a maximum post-0.73 Ma uplift of ~ 290 m in the SE Eifel. Here, we propose a new interpretation of the incision data of the intra-massif streams, where anomalies in the terrace profiles would result from knickpoint retreat in the tributaries of the main rivers rather than from tectonic deformation. We also use additional geomorphological data referring to (1) deformed Tertiary planation surfaces, (2) the history of stream piracy that severely affected the Meuse basin in the last 1 Ma, and (3) incision data outside the Rhenish shield. A new map of the post-0.73 Ma uplift of the Rhenish shield is drawn on the basis of this enlarged dataset. It reduces the maximum amount of tectonic uplift in the SE Eifel to ~ 140 m and modifies the general shape of the uplift, namely straightening its E–W profile. It is also suggested that an uplift wave migrated across the massif, starting from its southern margin in the early Pleistocene and currently showing the highest intensity of uplift in the northern Ardennes and Eifel. These features seem to favour an uplift mechanism chiefly related to lithospheric folding and minimize the impact on the topography of a more local Eifel plume.  相似文献   

3.
The evidence of coseismic uplift on the dynamic, wave-dominated Hua-tung coast fringing the active Coastal Range (eastern Taiwan) has been equivocal, due to complex controls by wave and terrestrial sediment over morphological and ecological systems of the coast. This study, by applying radiocarbon dating methods, demonstrates coseismic-uplift nature of the coast by finding synchronously killed intertidal organisms (mostly boring shell Jouannetia sp.) stranded at different sites of the coast with distinct physiographic characters. Based on these data, together with evidence from wave-cut notch sequences, two coseismic-uplift systems are recognized. One centers around the northern-middle part of the coast and yields events with uplift amounts of maximal 3–6 m and an average recurrence interval of at least several hundred years. The most recent activity of this system, influencing at least 70 km of coast, occurred at ~ 0.9 ka. The earthquake generating this event also triggered extensive landslides/debris flows in the region. Another system, exemplified by the uplift associated with the 2003 Cheng-kung earthquake, centers on the southern part of the coast and yields uplift of likely < 1 m every < 0.2 ky. Two pre-historic events of this system are identified as occurring at ~ 0.7 ka and ~ 1.1 ka. These two coseismic-uplift systems are consistent in position with two anticlinal structures defined by long-term uplift of the coast. However, the areas subjected to maximal coseismic uplift are located off where the climaxes of long-term uplift occur, implying that the latter areas have been uplifted mainly by aseismic and/or relatively frequent/small-magnitude coseismic motion.  相似文献   

4.
The great Indian Ocean earthquake of December 26, 2004 caused significant vertical changes in its rupture zone. About 800 km of the rupture is along the Andaman and Nicobar Islands, which forms the outer arc ridge of the subduction zone. Coseismic deformation along the exposed land could be observed as uplift/subsidence. Here we analyze the morphological features along the coast of the Andaman and Nicobar Islands, in an effort to reconstruct the past tectonics, taking cues from the coseismic effects. We obtained radiocarbon dates from coastal terraces of the island belt and used them to compute uplift rates, which vary from 1.33 mm yr− 1 in the Little Andaman to 2.80 mm yr− 1 in South Andaman and 2.45 mm yr− 1 in the North Andaman. Our radiocarbon dates converge on  600 yr and  1000 yr old coastal uplifts, which we attribute to the level changes due to two major previous subduction earthquakes in the region.  相似文献   

5.
The Northwestern (Maghreb) boundary of the Nubia (Africa) Plate   总被引：1，自引：0，他引：1  
Alain Mauffret   《Tectonophysics》2007,429(1-2):21-44
A study of the present compressional deformation of the Northwestern (Maghreb) Nubia (Africa) margin is derived from the analysis of more than 20,000 km of seismic profiles. In the western part the compression is distributed in a large zone with on-land compression in Algeria, mainly strike-slip deformation on the Algerian margin and folds and strike-slip faulting in Eastern Spain. In the middle of the Algerian margin, around Algiers, the evidences of compression become more obvious. In this area a ridge trending N–S that is interpreted as a middle to late Miocene spreading center interacted with the transpressional margin that trends E–W. North of the location of the Boumerdes–Zemmouri earthquake the oceanic crust is deformed by blind thrusts up to 60 km from the coast. These thrusts are south dipping and with the northward dipping thrusts located onshore form a wedge that maybe a positive flower structure at a crustal scale related to the right-lateral transpression of the margin. In the eastern part of the Northwestern (Maghreb) Nubia (Africa) Deformed Belt, off eastern Algeria and Tunisia, the deformation is more intense but limited to the north by the continental slope. Large late Miocene Tortonian folds are cut by the Messinian erosional surface but the present deformation is also evident. It is suggested that the deformation with a double vergence may be followed up to the north of Sicily. After the docking (18 Ma) of the Kabylies to the Africa Plate, the crust has been thinned and the Algerian Basin opened during the middle-late Miocene with an E–W direction. From the late Miocene to the Present the margin has been rethickened by transpression and uplifted.  相似文献   

6.
On Tuesday, November 17, 2015 at 07:10:07 (UTC) a strong earthquake struck Lefkas Island (Ionian Sea, Western Greece) with magnitude Mw 6.4, depth of about 6 km and epicenter located 20 km southwest of Lefkas town. It was felt in Lefkas Island and the surrounding region and caused the death of two people, the injury of eight others, many earthquake environmental effects (EEE) and damage to buildings and infrastructures. Secondary EEE were observed in western Lefkas and classified as ground cracks, slope movements and liquefaction phenomena. Primary effects directly linked to surface expression of seismogenic source were not detected in the field. The maximum intensity VIIIESI 2007 was assigned to large-volume slope movements along western coastal Lefkas. Damage to buildings was mainly observed in villages located in Dragano-Athani graben arranged almost parallel to the northern segment of the Cephalonia Transform Fault Zone (Lefkas segment). Among structures constructed with no seismic provisions, the stone masonry buildings and monumental structures suffered most damage, while the traditional buildings of the area with dual structural system performed relatively well and suffered minor damage. Reinforced-concrete buildings were affected not so much by the earthquake itself but by the generation of secondary EEE. The maximum seismic intensities VIIIEMS-98 were assigned to villages located in Dragano-Athani graben due to very heavy structural damage observed on masonry buildings mainly attributed to the combination of the recorded high PGA values, the poor antiseismic design and construction of buildings and the geological and tectonic structure of the affected area.  相似文献   

7.
A combination of published and new radiometric dates on uplifted Holocene fossil beaches from northeastern Sicily and southern Calabria (southern Italy) is compared with the altitude of the inner margin of the Last Interglacial (LIg) (Late Pleistocene, 124 ka) and older marine terraces in order to gain a regional-scale outline of uplift rates and their temporal changes in a region which is one of the fastest uplifting sectors of the Central Mediterranean Sea. Late Holocene radiocarbon dates from Ioppolo (southern Calabria) and Ganzirri (northeast Sicily), two newly discovered sites are here presented for the first time. The Holocene uplift rates are highest at St. Alessio and Taormina in eastern Sicily (2.4 mm/y) and at Scilla in southwestern Calabria (2.1 mm/y), two sites located across the Messina Straits and which separate the island of Sicily from mainland Italy. Uplift rates decrease towards the south and north from this centre of uplift. Late Holocene uplift rates show an apparent increase of between 64 and 124% when compared with the longer-term uplift rates calculated from the LIg highstand terraces. Furthermore, we discovered that the locations of fastest Late Pleistocene and Late Holocene uplift rates spatially coincide. To what extent the Holocene increase in uplift rates results from incomplete elastic strain release along the major extensional faults which frame the seismotectonic of the area, or indicate a true change in regional tectonic processes, is not resolved. Nonetheless, the heterogeneity of uplift, with a well-defined centre that crosses the Messina Straits, and its persistence at different time-scales indicates a tight connection between wider regional processes and fault-related displacement in controlling crustal instability in this area.  相似文献   

8.
The Egion earthquake which occurred in the Gulf of Corinth, central Greece (Ms = 6.2) on 15 June 1995 was caused by normal slip on the north-dipping and WNW-trending Egion fault. The Egion fault ruptured at depth during the Egion mainshock and probably re-ruptured at shallow level during the largest aftershock. The surface trace of the Egion fault has a segmented geometry. Linkage between three segments, which show long-term deformation differences as well as coseismic segmentation, enabled all segments to be incorporated in an earthquake segment. The surface ruptures continued to grow after the coseismic motion; the afterslip throw of the fault 10 weeks after the main event was equal to the 3 cm value for maximum coseismic slip. This afterslip was accompanied by uplift of the footwall block and a warp-like hangingwall subsidence (folding). This pattern of deformation was associated with more complex deformation at the western end of the earthquake segment. Here, afterslip was accompanied by general subsidence of the whole area (between 25th June and 30th July), followed by uplift of the whole area without afterslip (between 30th July and 2nd September). The afterslip-rate averaged over the 73 day period after the main event varied from 0.48 mm day−1 along the central part of the earthquake segment to 0.16 mm day−1 at the eastern end of the earthquake segment.  相似文献   

9.
We estimate current vertical movements along the Apennines (Italy) through repeatedly measured high precision levelling routes. In order to highlight regional crustal deformation the analysis of a geodetic database, with a minimum benchmark density of 0.7 bm/km (1943–2003 time period), is carried out. We evaluate systematic and random error and their propagation along the levelling routes. Tests on original raw height data have been carried out to define error propagation. The computed relative vertical rates stand significantly above error propagation. A series of traverses along and across the Apennines and a map of relative vertical velocities reveal a geodetic signal characterised by values up to 2.5–3.0 mm/a and by wavelengths up to 100 km.  相似文献   

10.
The western retroarc of the Southern Andes between 38° and 40° S is formed by a NNW-elongated ridge not associated with stacked thrust sheets. On the contrary, during the last 4–3 Ma this ridge was affected by extensional deformation, regional uplift and related folding on a very broad scale. Receiver function analysis shows that the drainage divide area and adjacent retroarc lie over an attenuated crust. Expected crustal thickness at these latitudes is around 38 km, whereas in this part of the retroarc the thickness is less than 32 km. The causes for such attenuation have been linked to a moderate steepening of the subducted Nazca plate beneath the South American plate, which is suggested by a westward shift and narrowing of the magmatic arc during the last 4 to 5 Ma. Gravimetric studies show that the upper plate did not react homogeneously to slab steepening, but ancient sutures and lithospheric discontinuities deeply buried under Mesozoic to Cenozoic sequences in the retroarc were locally reactivated. These processes resulted in an asthenospheric anomaly that correlates at the surface with the area of Pliocene to Quaternary doming, widespread extension and three radial troughs. Two of the troughs have accommodated substantial amounts of extension, but the third was probably aborted at an early stage. Moreover, the presence of an anomalous concentration of calderas and large volcanic centers over the proposed asthenospheric anomaly, and their age distribution, may indicate minor migration of the asthenospheric anomaly between 4 and 2 Ma through the western South American plate.  相似文献   

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