Depth and morphology of reflectors from the non-linear inversion of arrival-time and waveform semblance data. Part I: method and applications to synthetic data

We propose a two-dimensional, non-linear method for the inversion of reflected/converted traveltimes and waveform semblance designed to obtain the location and morphology of seismic reflectors in a lateral heterogeneous medium and in any source-to-receiver acquisition lay-out. This method uses a scheme of non-linear optimization for the determination of the interface parameters where the calculation of the traveltimes is carried out using a finite-difference solver of the Eikonal equation, assuming an a priori known background velocity model. For the search for the optimal interface model, we used a multiscale approach and the genetic algorithm global optimization technique. During the initial stages of inversion, we used the arrival times of the reflection phase to retrieve the interface model that is defined by a small number of parameters. In the successive steps, the inversion is based on the optimization of the semblance value determined along the calculated traveltime curves. Errors in the final model parameters and the criteria for the choice of the best-fit model are also estimated from the shape of the semblance function in the model parameter space. The method is tested and validated on a synthetic dataset that simulates the acquisition of reflection data in a complex volcanic structure. This study shows that the proposed inversion approach is a valid tool for geophysical investigations in complex geological environments, in order to obtain the morphology and positions of embedded discontinuities.     

The rotation of Italy: Preliminary palaeomagnetic data from the Umbrian sequence,Northern Apennines

A preliminary collection of 43 palaeomagnetic samples (10 sites) from the miogeosynclinal and supposedly autochthonous Umbrian sequence in the Northern Apennines, Italy, was analysed by means of alternating magnetic fields and thermal demagnetization studies. The older group of samples, taken from the upper part of the Calcari Diasprini (Malm), the Fucoid Marls (Albian/Cenomanian) and from the basal part of the Scaglia Bianca (Early Late Cretaceous), all showed normal polarity directions and resulted in a mean site direction:D = 290.5°,I = +51.5°,α₉₅ = 11°,k = 74,N = 4.The younger group of samples, taken throughout the Scaglia Rossa sequence (Latest Cretaceous/Middle Eocene) showed normal and reversed polarity directions. In contrast to the older group, the magnetic analysis of these samples resulted in a considerably less dense grouping of site mean directions. This presumably is due to inaccuracies introduced with the very large bedding tilt corrections that had to be applied to the samples of some sites. A tentative mean site direction for these Scaglia Rossa samples was computed as:D = 351°,I = +52.5°,α₉₅ = 23.5°,k = 11.5,N = 5.Despite the low precision of the Scaglia Rossa result, the significant deviation between this Latest Cretaceous/Early Tertiary direction and the Late Jurassic/Early Late Cretaceous direction indicates a counterclockwise rotation of more than forty degrees. This rotation can be dated as Late Cretaceous.How far these data from the Northern Apennines apply to other parts of the Italian Peninsula has yet to be established. The timing of this rotation is not at variance with the data from other parts of Mediterranean Europe (Southern Alps, Iberian Peninsula) and from Africa. However, taking into account the preliminary nature of the results, the amount of rotation of the Northern Apennines seems to surpass the rotation angle which is deduced from the palaeomagnetic data for Africa.     

A joint inversion algorithm to process geoelectric and surface wave seismic data. Part II: applications

Seismic and geoelectric methods are often used in the exploration of near-surface structures. Generally, these two methods give, independently of one other, a sufficiently exact model of the geological structure. However, sometimes the inversion of the seismic or geoelectric data fails. These failures can be avoided by combining various methods in one joint inversion which leads to much better parameter estimations of the near-surface underground than the independent inversions. In the companion paper (Part I: basic ideas), it was demonstrated theoretically that a joint inversion, using dispersive Rayleigh and Love waves in combination with the well-known methods of DC resistivity sounding, such as Schlumberger, radial dipole-dipole and pole-pole arrays, provides a better parameter estimation. Two applications are shown: a five layer structure in Borsod County, Hungary, and a three-layer structure in Thüringen, Germany. Layer thicknesses, wave velocities and resistivities are determined. Of course, the field data sets obtained from the ‘real world’ are not as complete and as good as the synthetic data sets in the theoretical Part I. In both applications, relative model distances, in percentages, serve as quality control factors for the different inversions; the lower the relative distance, the better the inversion result. In the Borsod field case, Love wave group slowness data and Schlumberger, radial dipole-dipole and pole-pole (i.e two-electrode) data sets are processed. The independent inversion performed using the Love wave data leads to a relative model distance of 155%. An independent Schlumberger inversion results in 41%, a joint geoelectric inversion of all data sets in 15%, a joint inversion of Love wave data and all geoelectric data sets in 15% and the robust joint inversion of Love wave data and the three geoelectric data sets in 10%. In the Thüringen field case, only Rayleigh wave group slowness data and Schlumberger data were available. The independent inversion using Rayleigh wave data results in a relative model distance of 19%. The independent inversion performed using Schlumberger data leads to 34%, the joint and robust joint inversion of Rayleigh wave and Schlumberger data gave results of 18% and 20%, respectively.     

3D v_P and v_S models of southeastern margin of the Tibetan plateau from joint inversion of body-wave arrival times and surface-wave dispersion data

A new 3D velocity model of the crust and upper mantle in the southeastern(SE) margin of the Tibetan plateau was obtained by joint inversion of body-and surface-wave data. For the body-wave data, we used 7190 events recorded by 102 stations in the SE margin of the Tibetan plateau. The surface-wave data consist of Rayleigh wave phase velocity dispersion curves obtained from ambient noise cross-correlation analysis recorded by a dense array in the SE margin of the Tibetan plateau. The joint inversion clearly improves the v S model because it is constrained by both data types. The results show that at around 10 km depth there are two low-velocity anomalies embedded within three high-velocity bodies along the Longmenshan fault system. These high-velocity bodies correspond well with the Precambrian massifs, and the twolocated to the northeast of 2013 M S7.0 Lushan earthquake are associated with high fault slip areas during the 2008 Wenchuan earthquake. The aftershock gap between 2013 Lushan earthquake and 2008 Wenchuan earthquake is associated with low-velocity anomalies, which also acts as a barrier zone for ruptures of two earthquakes. Generally large earthquakes(M≥5) in the region occurring from2008 to 2015 are located around the high-velocity zones,indicating that they may act as asperities for these large earthquakes. Joint inversion results also clearly show that there exist low-velocity or weak zones in the mid-lower crust, which are not evenly distributed beneath the SE margin of Tibetan plateau.     

Fault growth by segment linkage in seismically active settings: Examples from the Southern Apennines, Italy, and the Coast Ranges, California

Most models for fault growth and scaling are based on analysis of faults which display dip-slip (i.e. reverse, normal) and strike-slip kinematics; by contrast, little information is derived from faults displaying oblique-slip kinematics. Observations on mesoscopic transpressional faults from the Salinian Block of California and transtensional faults from the Southern Apennines of Italy reveal a complex kinematic history of fault propagation. Faults initially nucleate as isolate segments, which are later kinematically and mechanically linked via development of diffuse deformation zones and/or localised oblique connecting splays. The geometry of observed mesoscopic faults is similar to that of the host, larger structures, thus suggesting that the produced fault patterns are scale independent. Moreover, the overprinting relationships among minor fault-related fabrics permit to define a relative chronology within fault arrays, thus enabling a general sequence of structural stages to be correctly established. Based on minor fabrics and their overprinting relationships, a kinematic deformation model of fault growth by segment linkage is presented, which may have a wide applicability in the field of seismic hazard evaluation.     

2D modelling of resistivity and magnetotelluric data from the Belvedere Spinello salt mine,Italy1

The Belvedere Spinello salt mine is located in the Catanzaro Province of Calabria in Southern Italy. An extensive mining program has caused the development of Underground cavities filled with brine and the migration of this brine has been of great environmental concern to the mine owners. This paper presents the results of a multidimensional interpretation of a two-phase resistivity and magnetotelluric (MT) survey that was performed in an attempt to determine the complex conductivity structure of the mine area and to gain information on brine development and migration pathways. Key resistivity soundings were interpreted using a 2.5D algorithm based on the Polozhii decomposition method. The MT data were interpreted using a 2D finite-element code. A conductivity model was developed, integrating available geological and drill-hole information. The interpretation of the MT data, collected five years after the acquisition of the resistivity data, shows a conductive feature of depth that is not resolved in the resistivity interpretation. This feature has been interpreted as a thick brine zone that has developed as a result of mining during the interval between the resistivity and the MT measurements.     

综合近震及远震波形反演2006文安地震（Mw5.1）的震源机制解

2006年7月4日,在距离北京100 km左右的文安地区,发生了Mw=5.1级地震,引起了北京地区的强烈震感.为了更好的认识区域构造,我们利用近震及远震波形反演的方法得到了此次文安地震的震源机制.选择了北京数字地震台网的9个地震台,震中距小于600 km,台站的方位角覆盖较好.为了更好地利用信号相对较弱的P波信号,对于一个地震记录,本文分别截取出P波和面波两个部分,分别给予不同的权重进行反演,结合格点搜索的方法,得到了与记录P波及面波三分量对应较好的地震的方位角、倾角和滑移角.同时考虑到北京西北地区地壳较厚,本文在利用F-K方法计算近震理论波形的时候,对不同的方位角,采用了不同的地壳速度模型.随后结合远震信号中的直达P、pP、sP波形得到了分辨率较高的地震震源深度.反演结果表明,此次文安地震是一个较为典型的走滑型地震,方位角为210°,倾角80°,滑移角-150°,地震的深度为14～15 km,地震的震级为(Mw-5.1).反演结果与断层的几何分布、余震分布及北京地区北北东向应力场有很好的一致性.     

New algorithms of emission tomography for passive seismic monitoring of a producing hydrocarbon deposit: Part II. Results of real data processing

Two new algorithms of seismic emission tomography and the results of their numerical testing are presented. The algorithms allow eliminating of the screening effect caused by spatially correlated noise, and imaging of deep weak sources. Both algorithms invoke spatial filters, calculated on the basis of singular decomposition of the spectral matrix of the wave field. The key parameter of such a filter is the number of eigenvectors of the spectral matrix, which must be rejected in the process of seismic emission imaging in order to eliminate the screening effect. Consecutive increasing in the number of rejected eigenvectors enables imaging of ever weaker seismic sources.     

GIS‐assisted modelling for debris flow hazard assessment based on the events of May 1998 in the area of Sarno,Southern Italy: II. Velocity and dynamic pressure

The velocity and dynamic pressure of debris flows are critical determinants of the impact of these natural phenomena on infrastructure. Therefore, the prediction of these parameters is critical for hazard assessment and vulnerability analysis. We present here an approach to predict the velocity of debris flows on the basis of the energy line concept. First, we obtained empirically and field‐based estimates of debris flow peak discharge, mean velocity at peak discharge and velocity, at channel bends and within the fans of ten of the debris flow events that occurred in May 1998 in the area of Sarno, Southern Italy. We used this data to calibrate regression models that enable the prediction of velocity as a function of the vertical distance between the energy line and the surface. Despite the complexity in morphology and behaviour of these flows, the statistical fits were good and the debris flow velocities can be predicted with an associated uncertainty of less than 30% and less than 3 m s^?1. We wrote code in Visual Basic for Applications (VBA) that runs within ArcGIS^® to implement the results of these calibrations and enable the automatic production of velocity and dynamic pressure maps. The collected data and resulting empirical models constitute a realistic basis for more complex numerical modelling. In addition, the GIS implementation constitutes a useful decision‐support tool for real‐time hazard mitigation. Copyright © 2008 John Wiley & Sons, Ltd.     

Sensitivity analysis and application of time‐lapse full‐waveform inversion: synthetic testing and field data example from the North Sea,Norway

Time‐lapse refraction can provide complementary seismic solutions for monitoring subtle subsurface changes that are challenging for conventional P‐wave reflection methods. The utilization of refraction time lapse has lagged behind in the past partly due to the lack of robust techniques that allow extracting easy‐to‐interpret reservoir information. However, with the recent emergence of the full‐waveform inversion technique as a more standard tool, we find it to be a promising platform for incorporating head waves and diving waves into the time‐lapse framework. Here we investigate the sensitivity of 2D acoustic, time‐domain, full‐waveform inversion for monitoring a shallow, weak velocity change (?30 m/s, or ?1.6%). The sensitivity tests are designed to address questions related to the feasibility and accuracy of full‐waveform inversion results for monitoring the field case of an underground gas blowout that occurred in the North Sea. The blowout caused the gas to migrate both vertically and horizontally into several shallow sand layers. Some of the shallow gas anomalies were not clearly detected by conventional 4D reflection methods (i.e., time shifts and amplitude difference) due to low 4D signal‐to‐noise ratio and weak velocity change. On the other hand, full‐waveform inversion sensitivity analysis showed that it is possible to detect the weak velocity change with the non‐optimal seismic input. Detectability was qualitative with variable degrees of accuracy depending on different inversion parameters. We inverted, the real 2D seismic data from the North Sea with a greater emphasis on refracted and diving waves’ energy (i.e., most of the reflected energy was removed for the shallow zone of interest after removing traces with offset less than 300 m). The full‐waveform inversion results provided more superior detectability compared with the conventional 4D stacked reflection difference method for a weak shallow gas anomaly (320 m deep).     

GIS‐assisted modelling for debris flow hazard assessment based on the events of May 1998 in the area of Sarno,Southern Italy: Part I. Maximum run‐out

Based on the debris flow events that occurred in May 1998 in the area of Sarno, Southern Italy, this paper presents an approach to simulate debris flow maximum run‐out. On the basis of the flow source areas and an average thickness of 1·2 m of the scarps, we estimated debris flow volumes of the order of 10⁴ and 10⁵ m³. Flow mobility ratios (ΔH/L) derived from the x, y, z coordinates of the lower‐most limit of the source areas (i.e. apex of the alluvial fan) and the distal limit of the flows ranged between 0·27 and 0·09. We performed regression analyses that showed a good correlation between the estimated flow volumes and mobility ratios. This paper presents a methodology for predicting maximum run‐out of future debris flow events, based on the developed empirical relationship. We implemented the equation that resulted from the calibration as a set of GIS macros written in Visual Basic for Applications (VBA) and running within ArcGIS. We carried out sensitivity analyses and observed that hazard mapping with this methodology should attempt to delineate hazard zones with a minimum horizontal resolution of 0·4 km. The developed procedure enables the rapid delineation of debris flow maximum extent within reasonable levels of uncertainty, it incorporates sensitivities and it facilitates hazard assessments via graphic user interfaces and with modest computing resources. Copyright © 2007 John Wiley & Sons, Ltd.     

Analysis and interpretation of anomalous conductivity and magnetic permeability effects in time domain electromagnetic data: Part II: Sμ-inversion

In the paper by Pavlov and Zhdanov [J. Appl. Geophys. (2001)], we demonstrated that anomalous magnetic permeability of an ore body could result in measurable anomalous effects in TDEM data, which can be used in geophysical exploration. In the current paper, we develop a new method of TDEM data interpretation, which allows simultaneous reconstruction of both electrical and magnetic properties of the rocks. The method is based on a generalization of the S-inversion technique [66th Ann. Int. Mtg., Soc. Expl. Geophys., Expanded Abstr. (1996) 1306; 68th Ann. Int. Mtg., Soc. Expl. Geophys., Expanded Abstr. (1998) 473; J. Appl. Geophys. (1999)] for models containing thin sheets with anomalous conductivity and anomalous magnetic permeability. We call this method Sμ-inversion. Numerical 3-D modeling results demonstrate that Sμ-inversion provides useful information about both subsurface conductivity and magnetic permeability distributions. It can be used as a new tool for imaging TDEM data in mineral exploration.     

Site effects of the 2002 Molise earthquake, Italy: analysis of strong motion, ambient noise, and synthetic data from 2D modelling in San Giuliano di Puglia

On 31 October and 1 November 2002, the Basso Molise area (Southern Italy) was struck by two earthquakes of moderate magnitude (M _L = 5.4 and 5.3). The epicentral area showed a high level of damage, attributable both to the high vulnerability of existing buildings and to site effects caused by the geological and geomorphological settings. Specifically, the intensity inside the town of San Giuliano di Puglia was two degrees higher than in neighbouring towns. Also, within San Giuliano di Puglia, the damage varied notably. The site response in the city was initially evaluated from horizontal-to-vertical spectral ratios (HVSR) from a limited number of strong motion recordings of the most severe aftershocks. Several microtremor measurements were also available. Both data sets indicated the simultaneous presence of two amplification peaks: one around 6 Hz, attributed in previous studies to the strong, shallow impedance contrast among landfill/clay and calcarenites, and one at 2 Hz related to the first S-wave arrivals and predominantly seen only on one receiver component. Further studies performed on weak-motion recordings also showed strong amplification on the vertical receiver component, thus indicating an underestimation of the amplification by the HVSR technique. Additionally, a 2D-model of the geology of the sub-surface was developed, reproducing the flower-shaped structure generated during the late orogenic transpressive regime. The numerical (finite-difference hybrid) simulation reproduced the two peaks of the observed data at slightly higher frequencies. The model also confirmed that the borders of the flower structure define a boundary between amplification levels, with higher amplification inside.     

Investigation of topographic site effects using 3D waveform modelling: amplification,polarization and torsional motions in the case study of Arquata del Tronto (Italy)

Bulletin of Earthquake Engineering - The combined effect of topography and near-surface heterogeneities on the seismic response is hardly predictable and may lead to an aggravation of the ground...     

Landscape response to tectonic and climatic forcing in the foredeep of the southern Apennines,Italy: insights from Quaternary stratigraphy,quantitative geomorphic analysis,and denudation rate proxies

We present new data about the morphological and stratigraphic evolution and the rates of fluvial denudation of the Tavoliere di Puglia plain, a low‐relief landscape representing the northernmost sector of the Pliocene‐Pleistocene foredeep of the southern Apennines. The study area is located between the easternmost part of the southern Apennine chain and the Gargano promontory and it is characterized by several orders of terraced fluvial deposits, disconformably overlying lower Pleistocene marine clay and organized in a staircase geometry, which recorded the emersion and the long‐term incision history of this sector since mid‐Pleistocene times. We used the spatial and altimetric distribution of several orders of middle to late Pleistocene fluvial terraces in order to perform paleotopographic reconstruction and GIS‐aided eroded volumes estimates. Then, we estimated denudation rates on the basis of the terraces chronostratigraphy, supported by published OSL and AAR dating. Middle to upper Pleistocene denudation rates estimated by means of such an approach are slightly lower than 0.1 mm yr^‐1, in good agreement with short‐term data from direct and indirect evaluation of suspended sediment yield. The analysis of longitudinal river profiles using the stream power erosion model provided additional information on the incision rates of the studied area. Middle to late Quaternary uplift rates (about 0.15 mm yr^‐1), calculated on the basis of the elevation above sea level of marine deposits outcropping in the easternmost sector of the study area, are quite similar to the erosion rates average value, thus suggesting a steady‐state fluvial incision. The approach adopted in this work has demonstrated that erosion rates traditionally obtained by quantitative geomorphic analysis and k_sn estimations can be successfully integrated to quantify rates of tectonic or geomorphological processes of a landscape approaching steady‐state equilibrium. Copyright © 2014 John Wiley & Sons, Ltd.     

Structure and geological evolution of the island of Ponza, Italy: inferences from geological and gravimetric data

A geological and a geophysical survey have been carried out at Ponza Island, Tyrrhenian sea, Italy. Geological and structural data allowed to identify three main tectonic systems: NW-SE, NE-SW and E-W trending. The first one is related to a pre-volcanic tectonic event, probably linked to the Pliocene extensional activity of the Tyrrhenian evolution; the other two systems affected the volcanic units in two different stages of the Lower Pleistocene, the earlier one after the rhyolitic hyaloclastic formation (HF) emplacement and the later one after the emplacement of older trachytic pyroclastic deposits (Lower Pyroclastic Units—LPU). The latter event was followed by the emersion of the whole Ponza area, as testified by a marked erosional surface and marine terrace deposits cropping out at the top of LPU. The Upper Pyroclastic Units (UPU) represent the younger trachytic activity of the island (1.3 Myr) and do not show evidence of tectonic activity.The NW-SE-trending tectonic system probably assisted the rhyolitic magma rise, while the NE-SW- and E-W-trending systems mainly assisted the trachytic magma rise, responsible for the explosive and effusive activity in the southern area and for the hydrothermal fluids that caused alteration processes in the northern area.A 161-station gravimetric survey was carried out on the island and surrounding islets. The geological data and the gravimetric survey have been used to propose a 2.5 D model in which rhyolitic hyaloclastic deposits (ρ = 1.7 g cm⁻³) overlay an articulated Meso-Cenozoic sedimentary substratum (ρ = 2.6 g cm⁻³) laying at a depth to 300 m below sea level. Both formations are crossed by rhyolitic dykes (ρ = 2.4 g cm⁻³) which mark feeder fractures. In the M. Guardia area, where a maximum is present, this model accounts for the presence of a horst of the rigid basement, a shallow trachytic lava flow and its feeder (ρ = 2.8 g cm⁻³).     

Chemical structure and evolution of the mantle and continents determined by inversion of Nd and Sr isotopic data,II. Numerical experiments and discussion

Application of the inversion technique described in Part I [1] to models in which the depleted (MORB) mantle is created by extraction of continental crust results in a stable and self-consistent set of model data, including estimates of uncertainties on all the parameters. The inversion shows that the mean age of the continents (and of the depleted mantle) is 2.14–2.46 b.y., and that the lower crust must be depleted in Rb by a factor of ～ 4 relative to the upper crust. The fraction of total mantle which has been depleted ranges over wide limits (30–90%) depending on: (a) whether the lower mantle is considered to be virgin, or somewhat depleted; (b) whether the depleted reservoir is represented in Sm/Nd and Rb/Sr systematics by average values of MORB, or by extreme values of MORB, and (c) whether the bulk earth Nd content is presumed to be similar to E or H chondrites, or is higher than all known meteorite classes. The usefulness of crust-mantle budget models in constraining such questions as whole mantle versus two-layer mantle convection will be enhanced by better data and understanding in these three key areas of geochemistry.     

Eruption style and petrology of a new carbonatitic suite from the Mt. Vulture Southern Italy/: The Monticchio Lakes Formation

The Monticchio Lakes Formation MLF is a newly identified carbonatite-melilitite tuff sequence which is exposed in the southwestern sector of the Vulture volcano. It is the youngest example ca. 0.13 m.y. of this type of volcanism in Italy, although other carbonatites of smaller volume, but with similar characteristics, have been discovered recently. This volcanic event occurred in isolation after a 0.35 m.y. period of inactivity at Vulture. The eruption produced two maar-type vents and formed tuff aprons mainly composed of dune beds of lapilli. Depositional features suggest that a dry surge mechanism, possibly triggered by CO₂ expansion, was dominant during tuff emplacement. The MLF event involved a mixture of carbonatite and melilitite liquids which were physically separated before the eruption. Abundant mantle xenoliths are direct evidence of the deep-seated origin of the parental magma and its high velocity of propagation towards the surface. Often, these nodules form the core of lapilli composed of concentric shells of melilitite andror porphyritic carbonatite. Coarse-ash beds alternate with lapilli beds and consist of abundant lumps and spherulae of very fine-grained calcite immersed in a welded, highly compacted carbonatite matrix. Porphyritic carbonatite shells of the lapilli and fine-grained spherulae of calcite in the tuff matrix suggest incipient crystallisation of a carbonatite liquid in subvolcanic conditions and eruption of carbonatite-spray droplets. Dark coloured juvenile fragments mainly consist of melilite, phlogopite, calcite, apatite, perovskite, and häuyne crystals in a carbonatite or melilitite matrix. The rocks have an extremely primitive, ultramafic composition with very high Mga) 85. and Cr and Ni content 1500 ppm-. The calcite contains high SrO, BaO and REE of up to 1.5 wt.%. Similar compositions are typical of primary, magmatic carbonates which are found in both intrusive and extrusive carbonatites. The high modal Sr-Ba-REE-rich calcite, the typical mineralogy, and the high amount of Sr-group elements identify the carbonate component as a carbonatite. The very high Mga, mantle debris and C, O, He isotope ratios in the range of mantle values indicate a near-primary character for the carbonatite which is distinctive of a restricted group of extrusive carbonatites only found in continental rift areas.     

Contrasts in Tectonic style of the Central and Southern Appalachians, United States: Insights from seismic reflection data

Two reflection seismic transects, one across the central Appalachians in Virginia and the other across the southern Appalachians in Georgia, reveal a significant contrast in mid- and lower crustal reflectivity from east to west. Data from east of the Blue Ridge geologic province in Virginia and to the east of the Inner Piedmont in Georgia show a highly reflective crust extending from the near-surface to the Moho, including zones of east-dipping reflections, a sub-horizontal reflection signature at 7 seconds, and a west-dipping Moho. Reflection seismic data from west of the Blue Ridge in Virginia and Inner Piedmont farther south are characterized by reflector geometries related to deformation above a master decollement, leading to classic ‘thin-skinned’ tectonic structures in the overlying allochthon, and few if any apparent structures in the underlying basement. The location of the Iapetan rifted margin, the preexistence of favorably oriented structures to the east of this point, and sub-horizontal weak zones within the lower Paleozoic shelf strata have played critical roles in the distribution of seismic reflector geometry. Seismic reflection signatures seen in the southeastern United States are a result of multiple episodes of deformation from the early Paleozoic through the middle Mesozoic. Oblique stresses during late Paleozoic time produced transpression that manifested itself as predominantly strike-slip faulting to the east of the Blue Ridge/Inner Piedmont. Onlapping lower Paleozoic shelf strata responded to tectonic stresses through thin-skinned deformation above a master decollement during the late Paleozoic Alleghanian orogeny, aided in part by sub-horizontal zones of weakness in the strata. This partitioning of strain was supported via tectonic buttressing provided by Precambrian continental crust that was little deformed in the Taconic orogeny. During the Alleghanian orogeny, the variations in Valley and Ridge deformational style between the central and southern Appalachians were controlled by the original shape of the continental edge. Further deformation during Mesozoic extension occurred to the east of the Precambrian rift margin in the region where favorably oriented faults were reactivated, leading to the rotation of the fault zones from more steeply dipping initial orientations, the merging of the mid-crustal reflection zone with the Moho, and the formation of Mesozoic basins and antiformal reflections in the seismic sections.