Uplift Zone Research Articles

Evolution of collision-related basins in the eastern end of the Kurile Basin, Okhotsk Sea, Northwestern Pacific

A densely-meshed 9400 km long high-resolution seismic survey revealed the evolution of sedimentary basins in the southeastern rim of the Kurile Basin, offshore of eastern Hokkaido, NW Pacific. Hokkaido is situated in a collision zone not only of Okhotsk and Eurasian plates and also of the Kurile and NE Japan arcs. Offshore eastern Hokkaido is overlain by N–S-trending basins: Hamatonbetu-oki, Monbetu-oki, and Kitami-Yamato Sedimentary Basins (HOSB, MOSB and KYSB, respectively), and Abasiri-oki Trough (AOT), separated by zones of uplift. Depositional patterns of the HOSB and deformation of the adjacent Uplift Zone suggest the pull-apart origin of the basin related to dextral motions along the Central Sakhalin Fault, which extends to Hokkaido and binds the Okhotsk and Eurasian plates. The Uplift Zone adjacent to the MOSB suggests the initiation of subsidence in the Middle Miocene within a splay-fault basin with subsequent transformation into a 40 km wide graben in the Late Miocene and into a half graben in the Pliocene. The pre-late Miocene unconformity is widespread. The KYSB and the AOT began as a concatenated basin in the south of MOSB in the Middle Miocene. In the Pliocene, the Kitami’Yamato Bank (KYB) was uplifted and divided the KYSB–AOT basin into KYSB and AOT. The KYB uplift was probably induced by the Kurile forearc sliver movement. The interpretation of structures suggests that the Kurile Basin may have opened in a N–S-direction, from dextral shearing along a collision zone in the Middle Miocene. In the Pliocene, the kinematics changed to a NE–SE spreading direction; because of southwestward migration of the Kurile Arc with respect to the NE Japan Arc. Compressional tectonics after the Pliocene may suggest the destruction of the Kurile Basin.

Geological and biological evidence for regional drainage reversal during lateral tectonic transport, Marlborough, New Zealand

A 2500 km 2 mountainous river catchment in northern South Island, New Zealand, drained southwards until the late Quaternary. The catchment is being transported laterally at c . 36 mm a −1 relative to the southern South Island by dextral strike-slip motion along the Pacific–Australian Plate boundary (Alpine Fault). This lateral motion has moved the eastern half of the catchment from a zone of uplift into a zone of subsidence over the past million years, triggering drainage reversal. Sedimentation from the catchment switched from a sedimentary basin in the SE to a basin in the north. Profiles of river terrace remnants, formed from glacial outwash, show that drainage reversal occurred in the latter stages of deposition of the oldest recognizable terrace. Clast imbrication patterns and clast petrography in that terrace indicate southward flow, whereas flow had a northerly component in younger terraces and a nearby active river. In addition, 1.6% genetic divergence of fish on either side of the new drainage divide is consistent with late Quaternary separation by drainage reversal. The timing of drainage reversal is estimated from regional terrace correlation and the magnitude of the genetic divergence to be between 100 and 200 ka bp.

Effects of tectonics and lithology on long profiles of 16 rivers of the southern Central Massif border between the Aude and the Orb (France)

The analysis of longitudinal profiles of river channels and terraces in the southern Central Massif border, between the Aude and the Orb, allows the detection of anomalies caused by lithology and/or tectonic distortions. The rivers which have abnormally high slope and non-lithological knickzones indicate the main uplifted zones: the Montagne Noire and the Saint-Chinian ridge. A geomorphological and sedimentological analysis of detrital deposits was carried out as a basis for correlating the different formations, reconstructing the palaeodrainage and finding the main uplift and fluvial incision stages. During the Miocene, uplift remains limited as it is shown by the correlative fine deposits in the Languedocian piedmont. The Messinian incision (5.7–5.3 Ma) does not cross the Saint-Chinian ridge. On the other hand, fluvial incision becomes widespread in the Montagne Noire during the Upper Pliocene (3.4–2 Ma) when coarse deposits overlie either the Pliocene clay in the Orb palaeovalley or the Messinian conglomerates at the Cesse outlet. An Upper Pliocene uplift of the Montagne Noire and of the Saint-Chinian ridge is the cause of this incision and also of the diversion of the Cesse towards the Aude. Where the uplift rate was higher than incision rate, knickzones have developed like in the Avant-Monts south-side. The knickzones of lithological origin maintain a strong vertical stability during all the river incision stages. On the other hand, those of tectonic origin or base level lowering record upstream migration and their rate of retreat is controlled by the river discharge. As incision occurs only during the cold/temperate transition periods during the Quaternary, upward erosion slowly migrates (15 km since the Upper Pliocene, on the Orb) and so does not reach the riverheads.

Research on the dynamics of the South China Sea opening: Evidence from analogue modeling

Independent of Indochina extrusion, the South China Sea experienced a process from passive continental rifting to marginal sea drifting. According to the fault patterns in the Beibu Gulf basin and the Pearl River Mouth basin, the continental rifting and early spreading stage from 32 to 26 Ma were controlled by extensional stress field, which shifted clockwise from southeastward to south southeastward. From 24 Ma on, the sea spread in NW-SE direction and ceased spreading at around 15.5 Ma. Integrated geological information with the assumption that the South China Sea developed along a pre-Cenozoic weakness zone, we did analogue experiments on the South China Sea evolution. Experiments revealed that the pre-existing weakness zone goes roughly along the uplift zone between the present Zhu-1 and Zhu-2 depression. The pre-existing weakness zone is composed of three segments trending NNE, roughly EW and NEE, respectively. The early opening of the South China Sea is accompanied with roughly 150 clockwise rotation, while the SE sub-sea basin opened with SE extension. Tinjar fault was the western boundary of the Nansha block (Dangerous Ground), while Lupar fault was the eastern boundary of the Indochina, NW-trending rift belt known as Zengmu basin developed between above two faults due to block divergent of Indochina from Nansha. In the experiment, transtensional flower structures along NW-trending faults are seen, and slight inversion occurs along some NE-dipping faults. The existence of rigid massifs changed the orientations of some faults and rift belt, and also led to deformation concentrate around the massifs. The rifting and drifting of the South China Sea might be caused by slab pull from the proto South China Sea subducting toward Borneo and/or mantle flow caused by India-Asia collision.

Detection of ruptures of Andaman fault segments in the 2004 great Sumatra earthquake with coseismic ionospheric disturbances

Near‐field coseismic perturbations of ionospheric total electron content (TEC), caused by direct acoustic waves from focal regions, can be observed with Global Positioning System (GPS). They appear 10–15 min after the earthquake with typical periods of ∼4–5 min and propagate as fast as ∼1 km/s toward directions allowed by ambient geomagnetic fields. Ionospheric disturbance, associated with the 2004 December 26 great Sumatra‐Andaman earthquake, was recorded with nine continuous GPS receiving stations in Indonesia and Thailand. Here we explore the possibility to constrain the rupture process of the earthquake with the observed ionospheric disturbances. We assumed linearly distributed point sources along the zone of coseismic uplift extending ∼1300 km from Sumatra to the Andaman Islands that excited acoustic waves sequentially as the rupture propagate northward by 2.5 km/s. TEC variations for several satellite‐receiver pairs were synthesized by simulating the propagation of acoustic waves from the ground to the ionosphere and by integrating the TEC perturbations at intersections of line of sights and the ray paths. The TEC perturbations from individual point sources were combined using realistic ratios, and the total disturbances were compared with the observed signals. Prescribed ratios based on geodetically inferred coseismic uplifts reproduced the observed signals fairly well. Similar calculation using a rupture propagation speed of 1.7 km/s degraded the fit. Suppression of acoustic waves from the segments north of the Nicobar Islands also resulted in a poor fit, which suggests that ruptures in the northern half of the fault were slow enough to be overlooked in short‐period seismograms but fast enough to excite atmospheric acoustic waves. Coseismic ionospheric disturbance could serve as a new indicator of faulting sensitive to ruptures with timescale up to 4–5 min.

The role of the Béni floodplain on the chemical weathering fluxes in the upper Madeira basin, Bolivia

Institute GEMOC Key Centre, Department of Earth andPlanetary Sciences, Macquarie University, Sydney, NSW2109, AustraliaOn a global scale, several authors have reported good correla-tions between physical erosion fluxes and chemical weatheringfluxes (Gaillardet et al., 1999). This linkage have several origins,one being that the active floodplains can act as a biogeochemicalreactor in which the sediments produced in mountainous zonesand transported by the rivers, once deposited in foreland basins,are deeply weathered.We have tested this idea in the floodplain of the Rio Beni, inthe upper Madeira Basin, in Bolivia.Extreme physical denudation rates are found in the BolivianAndes, in particular due to the abundance of poorly lithifiedshales and of extensive outcrops of fluviolacustrine deposits inthe Upper Andes. These river sediments are exported and 40%is deposited in the foreland basin of the Beni R. where extensivefloodplains are submitted to wet tropical conditions.We compare here monthly collected river samples upstream(Rurrenabaque) and downstream (Riberalta) the Rio Beni flood-plain and averaged dissolved fluxes (over one year). Concentra-tions of major elements are corrected from atmospheric inputs.The main result is that the floodplain has almost no effect onthe chemical denudation rates of the Rio Beni, except loweringthem because of an increase in the drainage surface area.Although long-term weathering in the floodplain is more intensethan in the Andes, the flux of dissolved material released doesnot impact the Rio Beni chemical denudation rates. The differentelements show particular behavior that we will discussed in detail.We conclude that the foreland basin of the Rio Beni acts aboveall as a deposition area and does not contribute to the actualchemical weathering rates. This conclusion supports the idea thatchemical erosion is essentially active in mountainous areas andthat the high temperatures of the plain do not increase the chem-ical denudation rates. In the Beni river basin, tectonic character-istics (uplift and subsidence zone) appear as the first-orderfactors controlling chemical weathering fluxes.

Do river profiles record along‐stream variations of low uplift rate?

Spatial variations of gradients in landscapes may be used to identify and quantify recent deformation. The problem with doing this is to determine whether tectonic or climatic forcing is responsible for these variations, especially for low uplift rate environments (≪1 mm yr−1) where climate changes may have erased tectonic features. We evaluate the respective contribution of low uplift rate (∼0.1 mm yr−1) and Pleistocene climate oscillations on gradient variations of two comparable river profiles crossing different uplift zones in the southern Upper Rhine Graben. We compare the observed points of discontinuity in river profile (knickpoints) and convex portions (knickzones) with those predicted by a detachment‐limited model that includes stochastic short‐term and cyclic long‐term variations in climate, a bedrock detachment threshold and rock uplift. The detachment‐limited model is chosen as it predicts the development of persistent knickpoints. Differing values of the shear stress exponent, erosion threshold, climate variability and uplift pattern have been checked. Our modeling suggests that climate changes had no significant effects on profiles and that anomalies are more likely due to anticline growth. This surprising result arises from the combination of a very low regional uplift rate and the detachment‐limited assumption. The detachment‐limited model implies an upstream propagation of knickpoints and knickzones generated by uplift at the outlet during dry climate periods of low erosion. The greater the uplift rate, the larger the variations in river bed elevation. Thus, for high uplift rate, knickpoints and knickzones generated by climate oscillations are more likely to hide tectonic features. This result seems counterintuitive because it suggests that tectonic knickzones will be better preserved in low uplift rate environments, provided that the lithology is homogeneous.

Gold-Bearing Mesothermal Veins from the Gubong Mine, Cheongyang Gold District, Republic of Korea: Fluid Inclusion and Stable Isotope Studies

The Gubong deposit consists of five massive, gold-bearing mesothermal quartz veins that fill fractures oriented northeast and northwest along fault shear zones over an area of 14 km2 in Precambrian metasedimentary rocks of the Gyeonggi massif. The veins are divided into three groups, based on their orientation and location. They have a ribbon texture that is interpreted to result from repeated hydraulic fracturing events. Mineral deposition was associated with hydrothermal fluid overpressuring within and below the active fault shear zones. The vein mineralogy and paragenesis of the veins allow two separate discrete mineralization episodes to be recognized, separated by a major faulting event. The ore minerals are contained within quartz and calcite associated with fracturing and healing of veins that occurred during both mineralization episodes. Wall-rock alteration minerals during stage I, the main ore stage, include sericite, chlorite, and minor pyrite and carbonates. Sulfide minerals deposited along with electrum during this stage include arsenopyrite, pyrite, pyrrhotite, sphalerite, marcasite, chalcopyrite, galena, and argentite. Electrum also was deposited during stage II mineralization in the one group of veins, along with pyrite, sphalerite, chalcopyrite, and galena, but the second stage of deposition in other veins was barren. Petrographic examination of textural relationships among sulfides, fluid inclusions, microfracturing, and quartz shows chronological and genetic relationships between gold deposition and fluid entrapment. Systematic studies of fluid inclusions in stage I vein indicate two contrasting events: a relatively high temperature (203°–432°C) and pressure (943–2,098 bars) event related to early sulfide deposition and associated with H2O-CO2-CH4-NaCl ± N2 fluids (less than about 13.4 wt % NaCl), and a lower temperature (202°–399°C) and pressure (670–850 bars) late sulfide depositional event involving H2O-NaCl fluids (3.9–17.3 wt % NaCl). The H2O-NaCl fluid involved in ore-related stage II mineralization had a salinity of 0.4 to 4.2 wt percent NaCl and a homogenization temperature of 201° to 378°C. The calculated sulfur isotope compositions of hydrothermal fluids from the stage I veins (δ34SH2S = 3.5–10.5‰) indicate that ore sulfur was derived mainly from a magmatic source but also in part from sulfur contained in the host rocks. The calculated and measured oxygen and hydrogen isotope compositions of the ore-forming fluids (stage I: δ18OH2O = 1.1–9.0‰, δD = −92 to −21‰; stage II: δ18OH2O = −0.1 to +0.3‰, δD = −95 to −93‰) indicate that the fluids were derived from magmatic and/or deep-seated metasedimentary rocks (stage I) and evolved by mixing with local meteoric water (stage II), by limited water-rock exchange and by degassing during mineralization in uplift zones. The H2O-NaCl fluids involved in the stage I development of these veins represent fluids that evolved either through unmixing of H2O-CO2-CH4-NaCl ± N2 fluids following a decrease in fluid pressure or through mixing with deeply circulating meteoric waters, possibly as a result of uplift and/or unloading during mineralization. The H2O-NaCl fluid involved in stage II was derived from meteoric water. Early deposition of gold in stage I was caused by a decrease in sulfur fugacity (H2S loss) that accompanied the immiscible separation of carbonic vapor from H2O-CO2-CH4-NaCl ± N2 fluids. Gold in late stage I and stage II veins was precipitated from H2O-NaCl fluids by cooling and by dilution caused by mixing with meteoric water.

Crustal Velocity Structure and Seismic Activity in the Tianshan‐Pamir Conjunctive Zone

AbstractUsing recording data from a temporary seismic network, we obtained P wave velocity structure of the Tianshan‐Pamir conjunctive zone by tomographic inversion, revealing the heterogeneity of crustal structure and its relations to seismic activity. The results show that the collision between the Tianshan and Pamir caused strong crustal deformation on the western edge of the Tarim basin and resulted in basement uplift zones in the foreland areas. The crust is separated into several blocks by deep faults and some of them are wrapped within mountain belts. The deep crust of the Kashi depression has a relatively stable structure with less deformation, however, the crust of the Tianshan and western Kunlun shows a velocity feature of shortening and thickening, moreover, heating or thermal perturbation can be observed near the crust‐mantle boundary in the areas adjacent to the Tarim basin. Most earthquakes in this area are concentrated around high velocity blocks in the western end of the Tarim basin. We infer that the frequent earthquakes in the Tianshan‐Pamir conjunctive zone can be attributed to the interaction and stress adjustment between these blocks, while the earthquakes in the Jiashi area are related to the penetration of tectonic activity from Tianshan into the Tarim basin and the heterogeneous structure of the crust.

3D scattering image of the Campi Flegrei caldera (Southern Italy): New hints on the position of the old caldera rim

A scattering image of the Campi Flegrei caldera has been obtained using coda wave envelopes from local microearthquake data recorded at a portable 12-station digital network. This was operated during the paroxysmic phase of the ground uplift (bradyseism) that occurred in the years 1983–1984. The Nishigami technique has been used to obtain the 3D distribution of the strong scatterers in an earth volume with a horizontal extension of 20 km × 20 km and a vertical thickness of 6 km. This earth volume was segmented in blocks of 2 km × 2 km × 2 km for the outer section, and in blocks of 1 km × 1 km × 1 km for the inner section. The inversion was performed using a hybrid jackknife-SVD method that has allowed qualitative control of the stability and robustness of the solution. The results show that the scatterers revealed by the coda envelopes, which were band-pass filtered at a center frequency of 18 Hz, match the inner border of the caldera rim, which is well outlined on land by geological observations. The scatterer position also delineates this border well beneath sea level. These results are in close agreement with recently obtained seismic velocity tomography. The scatterers imaged at the 6 and 12 Hz band-pass frequencies are located around the zone of maximum uplift, beneath Solfatara crater, where most of the present residual volcanic activity is concentrated.

Continental-scale salt tectonics on Mars and the origin of Valles Marineris and associated outflow channels

Research Article| January 01, 2009 Continental-scale salt tectonics on Mars and the origin of Valles Marineris and associated outflow channels David R. Montgomery; David R. Montgomery † 1Quaternary Research Center, Department of Earth and Space Sciences, University of Washington, Seattle, Washington 98195-1310, USA, Astrobiology Program, University of Washington, Seattle, Washington 98195-1310, USA †E-mail: dave@ess.washington.edu Search for other works by this author on: GSW Google Scholar Sanjoy M. Som; Sanjoy M. Som 1Quaternary Research Center, Department of Earth and Space Sciences, University of Washington, Seattle, Washington 98195-1310, USA, Astrobiology Program, University of Washington, Seattle, Washington 98195-1310, USA Search for other works by this author on: GSW Google Scholar Martin P. A. Jackson; Martin P. A. Jackson 2Bureau of Economic Geology, Jackson School of Geosciences, The University of Texas at Austin, Austin, Texas 78713-8924, USA Search for other works by this author on: GSW Google Scholar B. Charlotte Schreiber; B. Charlotte Schreiber 3Quaternary Research Center, Department of Earth and Space Sciences, University of Washington, Seattle, Washington 98195-1310, USA Search for other works by this author on: GSW Google Scholar Alan R. Gillespie; Alan R. Gillespie 4Quaternary Research Center, Department of Earth and Space Sciences, University of Washington, Seattle, Washington 98195-1310, USA Astrobiology Program, University of Washington, Seattle, Washington 98195-1310, USA Search for other works by this author on: GSW Google Scholar John B. Adams John B. Adams 5Quaternary Research Center, Department of Earth and Space Sciences, University of Washington, Seattle, Washington 98195-1310, USA Search for other works by this author on: GSW Google Scholar GSA Bulletin (2009) 121 (1-2): 117–133. https://doi.org/10.1130/B26307.1 Article history received: 10 Aug 2007 rev-recd: 16 Feb 2008 accepted: 14 Mar 2008 first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation David R. Montgomery, Sanjoy M. Som, Martin P. A. Jackson, B. Charlotte Schreiber, Alan R. Gillespie, John B. Adams; Continental-scale salt tectonics on Mars and the origin of Valles Marineris and associated outflow channels. GSA Bulletin 2009;; 121 (1-2): 117–133. doi: https://doi.org/10.1130/B26307.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract A synthesis of deformation patterns within and around the Thaumasia Plateau, Mars, points to a new interpretation for regional deformation and the origin of Valles Marineris and associated outflow channels. The morphology of the Thaumasia Plateau is typical of thin-skinned deformation, akin to a “mega-slide,” in which extensional deformation in Syria Planum and Noctis Labyrinthus connects via lateral zones of transtension and strike-slip—Claritas Fossae and Valles Marineris—to a broad zone of compressional uplift and shortening defined by truncated craters and thrust faults along the Coprates Rise and Thaumasia Highlands. However, the low regional slope (~1°) results in gravitational body forces that are too small to deform the basaltic lava flows conventionally thought to compose the flanks of the Tharsis volcanic province. Instead, we conclude that geothermal heating and topographic loading of extensive buried deposits of salts and/or mixtures of salts, ice, and basaltic debris would allow for weak detachments and large-scale gravity spreading. We propose that the generally linear chasmata of Valles Marineris reflect extension, collapse, and excavation along fractures radial to Tharsis, either forming or reactivated as part of one lateral margin of the Thaumasia gravity-spreading system. The other, dextral, lateral margin is a massive splay of extensional faults forming the Claritas Fossae, which resembles a trailing extensional imbricate fan. The compressional mountain belt defined by the Coprates Rise and Thaumasia Highlands forms the toe of the “mega-slide.” Topographic observations and previous structural analyses reveal evidence for a failed volcanic plume below Syria Planum that could have provided further thermal energy and topographic potential for initiating regional deformation, either intrusively through inflation or extrusively through lava flow and/or ash fall emplacement. Higher heat flow during Noachian time, or geothermal heating due to burial by Tharsis-derived volcanic rocks, would have contributed to flow of salt deposits, as well as formation of groundwater from melting ice and dewatering of hydrous salts. We further propose that connection of overpressured groundwater from aquifers near the base of the detachment through the cryosphere to the martian surface created the outflow channels of Echus, Coprates, and Juventae chasmata at relatively uniform source elevations along the northern margin of the “mega-slide,” where regional groundwater flow would have been directed toward the surface. Our hypothesis provides a unifying framework to explain perplexing relationships between the rise of the Tharsis volcanic province, deformation of the Thaumasia Plateau, and the formation of Valles Marineris and associated outflow channels. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

ワシントン州, シアトル断層帯上における完新世海成段丘の高度分布と活断層との関係

A flight of late Holocene marine terrace fringes the central area of Puget Sound, and records uplift over an extensive area above the Seattle fault zone. The E-W trending blind thrust fault zone is a source of major seismic hazards in the Seattle metropolitan area. Gravity and seismic reflection surveys indicate a south- dipping fault plane, but its exact location and timing of past activities were unknown. LiDAR topographic mapping of the Puget lowland revealed several fault scarps on the glacial landscape hidden under the dense forest. We observed the fault, offset on the Holocene marine terrace surface and measured the former shoreline height at 97 locations using LiDAR DEM to map terrace deformation patterns and their relation to the faults. Studied areas include 1) Alki Point, 2) the southern part of Bainbridge Island, and 3) the southeastern Kitsap Peninsula near Port Orchard and southwestern Bainbridge Island. The height of the former shorelines marked by the Holocene terrace changes from ca. 10.7 to 7.3m a. s. l in the west to 12.2 to 10.1m in the east of the Toe Jam Hill fault, and 10.6 to 7.8m in the west to 9.7 to 7.9m in the east of the Waterman Point fault. These changes indicate differential uplift of the terrace surfaces across the faults. There are two newly identified faults in this study. One is the Point Glover fault that is marked by a scarp in the LiDAR map and associated 2m offset of the terrace surface. The other is the South Beach Point fault inferred by the northward tilt of the terrace surface. Because these faults strike E-W, parallel to the main Seattle Fault on its south side, and have south-facing scarps and north-dipping fault planes, they are probably back-thrsuts to the main Seattle Fault. The width of the backthrust zone is at least 4km. The age of the terraces approximately coincides with the most recent faulting event on the surface fault (at least for Toe Jam Hill Fault, ca. 1000yr BP), thus the differential uplift probably occurred simultaneously with fault movement. Although the surface backthrust scarps are less than a few kilometers long and vertical offset is 2-3m, the total amount of uplift reaches about 12m. Subtracting the effect of the vertical displacement and the amount of northward tilting, the uplift of several meters still remains on the Seattle fault zone of over about 4km wide. This broad zone of uplift is not due to the slip on the subsidiary backthrusts, but probably due to the blind thrust of the main Seattle fault. We infer that at least some of the coastal deformation is caused by broad surface upwarping above the Seattle fault and that the upwarping occurred at ca. 1000yrs BP, associated with ruptures on at least three of the backthrusts. The uplift and faulting may represent the largest earthquake in the Puget Sound area during the late Holocene.

Outline of vertical displacement of the 2004 and 2005 Sumatra earthquakes revealed by satellite radar imagery

Abstract Analyses of satellite radar imagery before and after the 2004 and 2005 Sumatra earthquakes reveal an overview of the uplift and submergence pattern of islands along the subduction zone and provide an outline of the regions that experienced coseismic vertical deformation. We find evidence of crustal deformation from the northern tip of the Andaman Islands to Nias Island. A line 145 km east of the trench separates western uplifted zone from eastern subsided zone. Agreement with the field observation demonstrates the feasibility of our method. We find that radar imagery analysis is more efficient for investigating vertical displacements than similar techniques using optical sensors.

Crustal Structure and Comparison of Different Tectonic Blocks in North China

The North China paleocontinenal block has undergone reconstruction through multi-stage tectonic movements, resulting in distinct characteristics of crustal subdivision. Based on data and study results of nearly 30 profiles of deep seismic sounding with a total length of about 20000km, we make a further study on the fine structures of the sub-blocks of the crust beneath North China and comparison of their differences. According to the structural features, the crust of North China can be classified into 3 types. The first is a simple crustal structure in the Ordos basin in the western part of the region, with an integrated basement structure, showing the crustal structure feature of stable paleocontinent. The second is a relatively simple crustal structure in the Taihang mountain located in the middle part, and the Yinshan mountain and Yanshan mountain in the northern part. These are uplifted zones where slight velocity reversal exists in local areas of the middle and lower crusts which is possibly related to medium decoupling deformation within the crust caused by the regional crustal thickening and uplifting. The third is a complex crustal structure in the rift-depression basin in the eastern part of North China, with a sinking and fragmentized basement, loosen media within the crust, low velocity, uplifted Moho, thinned crust, and obvious lateral structural differences, showing tectonic features of the newly reconstructed crust. Based on these analyses, we discuss the crustal block-subdivision tectonics and related dynamic evolution in North China in a comprehensive manner.

Plate-wide stress relaxation explains European Palaeocene basin inversions

During Late Cretaceous and Cenozoic times, many Palaeozoic and Mesozoic rifts and basin structures in the interior of the European continent underwent several phases of inversion (the process of shortening a previously extensional basin). The main phases occurred during the Late Cretaceous and Middle Palaeocene, and have been previously explained by pulses of compression, mainly from the Alpine orogen. Here we show that the main phases differed both in structural style and cause. The Cretaceous phase was characterized by narrow uplift zones, reverse activation of faults, crustal shortening, and the formation of asymmetric marginal troughs. In contrast, the Middle Palaeocene phase was characterized by dome-like uplift of a wider area with only mild fault movements, and formation of more distal and shallow marginal troughs. A simple flexural model explains how domal, secondary inversion follows inevitably from primary, convergence-related inversion on relaxation of the in-plane tectonic stress. The onset of relaxation inversions was plate-wide and simultaneous, and may have been triggered by stress changes caused by elevation of the North Atlantic lithosphere by the Iceland plume or the drop in the north-south convergence rate between Africa and Europe.

能登半島西方海域の新第三紀〜第四紀地質構造形成

The Noto Peninsula district is known as a N-S trending uplift zone in the Neogene Tertiary to Quaternary. A geological survey mainly composed of sonic prospecting was conducted in the west sea area of the Noto Peninsula. 8 units of stratum, in particular, 5 units in the Quaternary, were found clearly as acoustic stratigraphy. This made it possible to describe the geological development of the Neogene Tertiary to Quaternary of the district in more detail than has ever been reported. The study area can be divided into 2 areas. In the southern part, 2 bilaterally asymmetric folds that are relatively newly developed with a N-S trend have been formed probably by block movement. In the northern part, which is just the southwestern extension of Okunoto Hill, one of the typical tilted block mountains on Noto Peninsula, there are distributed 2 NE-SW trending tilted blocks accompanied by faulting. These tilted blocks have been uplifted by block movement. A relatively new uplift can be found in the block located in the extended part of the N-S trending fold. Consideration based on the facts above and reported show that the newly developed N-S trending geological structure of the Noto Peninsula district has been formed by block movement at least since the late Pliocene.

Seismological and geological characterization of the crust in the southern part of northern Fossa Magna, central Japan

The northern Fossa Magna (NMF) is a Miocene rift basin formed in the final stages of the opening of the Sea of Japan. The northern part of Itoigawa-Shizuoka Tectonic Line (ISTL) bounds the western part of the NMF and forms an active fault system that displays one of the largest slip rates in the Japanese islands. Reflection and refraction/wide-angle reflection profiling and earthquake observations by a dense array were undertaken across the northern part of ISTL in order to delineate structures in the crust, and deep geometry of the active fault systems. The ISTL active fault system at depth (ca. 2 km) shows east-dipping low-angle in Omachi and Matsumoto and is extended beneath the Central Uplift Zone and Komoro basin keeping the same dip-angle down to ca. 15 km. The upper part of the crust beneath the Central Uplift Zone is marked by the high Vp and high resistivity zone. Beneath the folded zone of the NMF, the middle to lower crust shows low Vp, low resistivity and more reflective features. The balanced geologic cross-section based on the reflection profiles suggests that the shortening deformation since the late Neogene was produced by the basin inversion of the Miocene low-angle normal fault.

Low Vp and Vp/Vs zone beneath the northern Fossa Magna basin, central Japan, derived from a dense array observation

The northern Fossa Magna (NFM) basin is a Miocene rift system formed in the final stage of the opening of the Japan Sea. The northern part of the Itoigawa-Shizuoka Tectonic Line (ISTL) bounds the western part of the northern Fossa Magna. In order to understand the active tectonics in these areas, it is essential to explain the seismic velocity structures, deep structures of active faults, and microseismicity near the active faults. In the autumn of 2002, we conducted a seismic array observation across the northern part of the ISTL and the NFM to obtain a structural image beneath the NFM. Arrival times of local earthquakes and explosive shots were used in a joint inversion for earthquake locations and 3-D Vp and Vp/Vs structures. P- and S-wave arrival time data were obtained from 73 events including 4 explosive shots, and 3809 P- and 2659 S-wave arrival times were used for the inversion analysis. We obtained a seismic velocity model revealing good correlations with the surface geology along the profile. In particular, we found thick low-velocity zones beneath the NFM and the Komoro basin and a high-velocity zone beneath the Central Uplift Zone. Beneath the NFM, a low-velocity zone with low-to-moderate Vp/Vs extends to a depth of approximately 10 km. The low-velocity suggests the existence of aqueous fluid-filled pores with high aspect ratios.

Enhancement of magnetic signatures of impact structures

Aeromagnetic surveys play an important role in the detection and analysis of terrestrial impact structures as large semi-regional aeromagnetic surveys are widely available. Impact craters can be divided into two groups based on morphostructure, namely simple and complex. Simple craters are relatively small bowl-shaped depressions with an upraised and fractured rim whereas complex craters are larger with a central uplift zone. Magnetic signatures of terrestrial impact craters vary greatly, reflecting the target rocks, the impact-related magnetisation and effects of crater fill and post-impact sediments. In basement rocks, the common signature is a magnetic low, ranging in amplitude from a few nT up to a few hundred nT. The central peak or ring uplift of crushed basement may produce strong magnetic highs. The magnetic signature may be due to shock demagnetisation, shock remagnetisation, and thermal and chemical remanent magnetisation effects. Impact craters in sedimentary targets are usually subdued and amplitudes of a few nT up to 10 nT are common. Enhancement of magnetic signatures of impact structures using filtering techniques is an important part of detection and analysis. Derivatives and shaded relief techniques, along with separation filtering, are probably the most used methods. Algorithms for fractional order derivatives and circular shaded relief have dramatically improved filter results. The fractional derivative order can be varied to optimise separation of the impact magnetic signature. Circular shaded relief treats all directions equally unlike the fade-out for features sub-parallel to the shading direction evident in conventional shading. The fractional order derivative and circular shaded relief algorithms are illustrated from impact structures in Australia and Canada in both basement and sedimentary cover rocks.

Density structure inferred from gravity anomalies in the eastern area of the Itoigawa-Shizuoka Tectonic Line, central Japan

A gravity survey was conducted between October 2002 and December 2003 in and around the eastern area of the Itoigawa-Shizuoka Tectonic Line (ISTL). The total number of measurement points amounted to about 436 and 326 stations were taken at the same points as the seismic survey points. The location and altitude were decided by differential GPS and the accuracy is thought to be within several ten-centimeters. The data was compiled from existing data (Geological Survey of Japan, 2000), so the total number of compiled gravity maps is about 3,540 points. All measured gravity data were referred to the International Gravity Standardization Net 1971 (IGSN71) and the normal gravity values were estimated according to the gravity formula of 1980. Terrain corrections were conducted within a range of 60 km by approximating the real topography to an assemblage of annular prisms interpolated by mesh terrain data and random terrain data of the gravity points. The effect of the sinking of the topography due to the Earth’s curvature was taken into consideration. Bouguer corrections within a range of 60 km in arc distances were made using a spherical cap crust formula. The density for both terrain correction and Bouguer corrections was chosen to be 2,670 kg/m3, because the mean surface density of the whole area is estimated to be a slightly large density by the CVUR method. The features of Bouguer anomalies is characterized by a low anomaly in Omachi city, in the northern parts of Matsumoto basin, and a high anomaly in the central highlands, Central Uplift Zone, about 10 km west of Ueda city. The low anomaly shows that the thickness of the sedimentary layer is more than 1 km from 2D/3D automatic analysis.