Recent vertical crustal movements from precise leveling surveys in the Blue Ridge and Piedmont Provinces, North Carolina and Georgia

Examination of two lines of repeated leveling in North Carolina and Georgia reveals

1. (1) apparent uplift at the Blue Ridge-Piedmont physiographic boundary (the AtlanticGulf drainage divide) relative to the Atlantic Coastal Plain on the east and the Valley and Ridge province to the west; and

2. (2) large tilts over short baselines superimposed upon the regional pattern in the vicinity of the nearby Blue Ridge—Piedmont geologic boundary (the Brevard fault zone). In the North Carolina profile a very pronounced correlation between topography and movement suggests possible systematic leveling error, but the observed movements appear to be larger than those normally attributed to leveling error. Thus, either refraction or rod errors are larger than expected, or the movement is real and strongly correlates with topography along this portion of the leveling line.

Anomalously high stream-gradients over both resistant and nonresistant lithologies are found around the drainage divide in North Carolina, and may be associated with the relative uplift inferred from releveling. The drainage divide in Georgia, also characterized by relative uplift on the movement profile, approximately separates two different types of stream patterns. In both cases evidence presented here suggests that stream morphology may be responding to contemporary deformation as implied by the observed elevation changes. The relative uplift in North Carolina also correlates with a positive Bouguer gravity anomaly of 30–40 mGal in the midst of the regional Blue Ridge gravity low, although the significance of the correlation is unclear.The close spatial correspondence between the zone of maximum uplift and the drainage divide suggests that the vertical movements and geomorphic anomalies may result from the same mechanism, although the nature of such is unclear. One possible mechanism could be displacement at depth along the nearby Brevard zone. However, on the basis of dislocation modeling it appears that the geodetic observations cannot be adequately explained by surface deformation associated with any simple models of slip on the Brevard zone.     

Recent vertical movements and their determination in the Rhenish Massif

The uplift of the Rhenish Massif started in late Tertiary time. The determination of the rates of recent vertical movements helps to interpret the whole, phenomenon. The data obtained by relevellings of high precision will be analysed by two different velocity models based on the concepts of Holdahl: the single-point model and the velocity surface model. Both models yield adjusted heights corresponding to a selected reference time and the velocities. The significance of the model parameters will be increased by introducing free adjustments with generalized inverses.     

Regional investigations of vertical crustal movements in the U.S., using precise relevelings and mareograph data

In the past two years, the National Geodetic Survey has been creating a data base of vertical crustal movement information. The data elements are relative elevation changes along lines of releveling which are used to produce graphic displays on microfilm. In separate studies, the releveling data, together with information extracted from mareograph records, have been used to create two networks of velocity differences. The two networks, one in the vicinity of Chesapeake Bay and the other covering the Gulf Coast states, have been adjusted in order to prepare maps showing the velocities of elevation change. In the adjustments, the velocities derived from mareograph records were treated as observations. The results indicate annual subsidence ranging between −1.2 mm and −4.0 mm in the Chesapeake Bay area, with significant local variation. In the Gulf Coast region there is generally slight subsi'dence along the coast, ranging between 0.0 and −1.5 mm/year. Stability and slight uplift is indicated to the north where bedrock reaches the terrain surface. Anomalous subsidence of −7.0 mm/year occurs at New Orleans, La., and at Houston, Texas, there has been several decimeters change in the last ten years.     

Recent stress field and neotectonics in the Eastern Jura Mountains,Switzerland

The regional stress field and its local variation were determined for the northern part of central Switzerland (Fig. 1) by using overcoring techniques (doorstopper, triaxial strain cell) and observations of breakouts in deep boreholes. The results are compared with fault plane solutions of earthquakes and with the orientation of horizontal stylolites.In the northern part of central Switzerland the NW-SE-orientation of the maximum horizontal stress (S_H) which is characteristic for Central Europe was observed only in the crystalline basement. In the Folded Jura and south of it in one well the greatest principal horizontal stress above the Triassic decollement horizon is oriented approximately in a N-S to NNE-SSW direction.This direction persists into the western Tabular Jura and the southernmost Rhine Graben. Only in the eastern part of the Tabular Jura the greatest principal horizontal stress shows a NNW-SSE to NW-SE orientation. Comparison of the near surface stress field as determined by in situ stress measurements and borehole breakouts with the directions of horizontal stylolites generated during the evolution of the Folded Jura, indicates that the orientation of the recent stress field near the earth's surface is the same as that which prevailed during the Upper Miocene to Lower Pliocene.The central part of northern Switzerland is therefore the first area in Central Europe where it is possible to demonstrate that the near surface stress field is decoupled from that in the crystalline basement. The difference in the orientation of the greatest principal horizontal stress is about 50°.     

Temporal variability of diverse mountain permafrost slope movements derived from multi-year daily GPS data,Mattertal, Switzerland

In this study, high resolution surface measurements of diverse slope movements are compared to environmental factors such as ground surface temperature (GST) and snow cover, in order to reveal and compare velocity fluctuations caused by changing environmental conditions. The data cover 2 years (2011–2013) of Global Positioning System (GPS) and GST measurements at 18 locations on various slope movement types within an alpine study site in permafrost (Mattertal, Switzerland). Velocities have been estimated based on accurate daily GPS solutions. The mean annual velocities (MAV) observed at all GPS stations varied between 0.006 and 6.3 ma^?1. MAV were higher in the period 2013 compared to 2012 at all stations. The acceleration in 2013 was accompanied by a longer duration of the snow cover and zero curtain and slightly lower GST. The amplitude (0–600 %) and the timing of the intra-annual variability were generally similar in both periods. At most stations, an annual cycle in the movement signal was observed, with a phase lag of 1–4 months to GST. Maximum velocity typically occurred in late summer and autumn, and minimum velocity in late winter and beginning of spring. The onset of acceleration always started in spring during the snowmelt period. At two stations located on steep rock glacier tongues, overprinted on the annual cycle, short-term peaks of velocity increase, occurred during the snowmelt period, indicating a strong influence of meltwater.     

Recent earth movements in the Middle East

In many sectors of the Alpine-Himalayan mountain system movement continues into recent times, but the rate of movement is usually uncertain. The Mesopotamian plains show the effect of movement on canal systems and on old culture levels. There is a regional up-warp of the mountains as a whole and a depression of the plains, but there is also continued growth of individual anticlines. The head of the Persian Gulf is now advancing and has inundated extensive areas which were under irrigated cultivation perhaps up to the 13th. century A.D. At Shaur an anticline was crossed by an old Sassanian canal which has since been folded at a rate of one metre per century.     

Integrated methods and scenario development for urban groundwater management and protection during tunnel road construction: a case study of urban hydrogeology in the city of Basel,Switzerland

In the northwestern area of Basel, Switzerland, a tunnel highway connects the French highway A35 (Mulhouse–Basel) with the Swiss A2 (Basel–Gotthard–Milano). The subsurface highway construction was associated with significant impacts on the urban groundwater system. Parts of this area were formerly contaminated by industrial wastes, and groundwater resources are extensively used by industry. During some construction phases, considerable groundwater drawdown was necessary, leading to major changes in the groundwater flow regime. Sufficient groundwater supply for industrial users and possible groundwater pollution due to interactions with contaminated areas had to be taken into account. A groundwater management system is presented, comprising extensive groundwater monitoring, high-resolution numerical groundwater modeling, and the development and evaluation of different scenarios. This integrated approach facilitated the evaluation of the sum of impacts, and their interaction in time and space with changing hydrological boundary conditions. For all project phases, changes of the groundwater system had to be evaluated in terms of the various goals and requirements. Although the results of this study are case-specific, the overall conceptual approach and methodologies applied may be directly transferred to other urban areas.     

Engineering geology of Mokattam city and vicinity, eastern Greater Cairo, Egypt

A highly jointed, highly fossiliferous, vuggy and sandy dolomitic limestone, the Ain Musa Bed, is the foundation bed rock of Mokattam city. The slopes southwestern sides of the Upper Plateau of Gebel Mokattam, where the city was built, have been affected by slope failure and retreat of the edge of the and a road have been damaged. A 55 m slope retreat took place between 1956 and 1989. A field model is proposed for the slope failure in this area where foundation bed rock are removed by erosion after swelling and flowing, which is due to saturation by leaking fresh and sewage water. The resulting unde bed rock leads to slope failure of large blocks where vertical joints act as potential failure surfaces. Several recommendations are proposed to decrea failure in the city.

The Upper Plateau of Gebel Mokattam is underlain by limestones of the Middle Plateau where a new suburb is being built. A comparison between the geolog properties of the foundation bed rocks of the Upper and Middle Plateaux indicates that the limestones of the latter are more suitable foundation bed ro with expansive clays and are composed of hard, micritic limestones with a few megafossils and no cavities. Rock mass properties are also different and are stable.     

Short-term vertical velocity field in the Apennines (Italy) revealed by geodetic levelling data

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.     

Seismic hazard assessment of the city of Hamedan and its vicinity, west of Iran

This article presents the results of deterministic and probabilistic seismic hazard analyses (DSHA and PSHA) of the city of Hamedan and its neighboring regions. This historical city is one of the developing cities located in the west of Iran. For this reason, the DSHA and PSHA approaches have been used for the assessment of seismic hazards and earthquake risk evaluation. To this purpose, analyses have been carried out considering the historic and instrumented earthquakes, geologic and seismotectonic parameters of the region covering a radius of 100?km, keeping Hamedan as the center. Therefore, in this research, we studied the main faults and fault zones in the study area and calculated the length and distance of faults from the center of Hamedan. In the next step, we measured the maximum credible earthquake (MCE) and peak ground acceleration (PGA) using both DSHA and PSHA approaches and utilized the various equations introduced by different researchers for this purpose. The results of DSHA approach show that the MCE-evaluated value is 7.2 Richter, which might be created by Nahavand fault activities in this region. The PGA value of 0.56?g will be obtained from Keshin fault. The results of PSHA approach show that the MCE-evaluated value is 7.6 Richter for a 0.64 probability in a 50-year period. The PGA value of 0.45?g will be obtained from Keshin fault. Seismic hazard parameters have been evaluated considering the available earthquake data using Gutenberg?CRichter relationship method. The ??a?? and ??b?? parameters were estimated 5.53 and 0.68, respectively.     

Earthquake focal mechanisms of the induced seismicity in 2006 and 2007 below Basel (Switzerland)

To stimulate the reservoir for a “hot dry rock geothermal project, that was initiated by a private/public consortium in the city of Basel, approximately 11500 m³ of water were injected between December 2nd and 8th, 2006, at high pressures into a 5 km deep well. More than 10500 seismic events were recorded during the injection phase, and minor sporadic seismic activity was still occurring more than two years later. The present article documents the focal mechanisms of the 28 strongest events, with M_L between 1.7 and 3.4, that have been obtained by the Swiss Seismological Service (SED) during and after the stimulation. The analysis is based on data that was recorded by a six-station borehole network, operated by the project developers, as well as by several permanent and temporary surface networks. The hypocenters of the events are located inside the stimulated rock volume at depths between 4 and 5 km within the crystalline basement. Of the 28 faultplane solutions two are normal faulting mechanisms and one is a strike-slip mechanism with a strong normal component. All others are typical strike-slip mechanisms with mostly NS and EW striking nodal planes. As a consequence, the T-axes are all nearly horizontal and oriented in a NE or SW direction (mean azimuth 46 ± 11 degrees) and the P-axes of the strike-slip events point in a NW or SE direction (mean azimuth 138 ± 13 degrees). Overall, the observed focal mechanisms agree with what would be expected from both the stress observations within the well and the stress field derived from the previously known natural seismicity.     

ShakeMap-based prediction of earthquake-induced mass movements in Switzerland calibrated on historical observations

Natural Hazards - In Switzerland, nearly all historical Mw?~?6 earthquakes have induced damaging landslides, rockslides and snow avalanches that, in some cases, also resulted in damage...     

Assessment of benchmark credibility in the study of recent vertical crustal movements

Results of repeated precise leveling in several regions indicate that the magnitude of inferred vertical displacements is controlled by the quality of benchmark monumentation. If ignored, such a correlation may lead to an erroneous tectonic interpretation of the computed pattern of motion.     

Recent crustal movements and the Moneron earthquake of 1971

From the results of high-precision levelling conducted in the southern part of Sakhalin Island, the dynamics of the earth's surface have been determined before the Moneron earthquake in 1971, during its numerous aftershocks and in the following periods. Great subsidence, of up to 7–8 cm, preceded the earthquake, then a 3-year period of steady state followed and at the end of this period the earthquake happened. After this event vertical movements show an inherited character related to the very recent geological structures. Horizontal displacements of the triangulation net, 50 km distant from the earthquake epicentre, were also noted; they had a northeast direction and an amplitude of 7 cm.     

Recent tectonic movements of the Costa Rican Pacific coast

An analysis of the bioerosional morphology of the Pacific coast of Costa Rica (Central America) indicates a recent uplifting of this coast. The uplift produces a framework of blocks, bordered by NE-SW-striking faults. The blocks were elevated to different heights, 1–2 m above their original position. The elevation ocurred in recent times. The coastal sector with uplifting tendency corresponds to the western border of an outer arc. Between this arc and an inner arc, a small zone of subsidence with drowned bioerosional morphologies can be observed.