Upper Silurian–Middle Devonian radiolarian zones of the Yokokurayama and Konomori areas in the Kurosegawa Belt, Southwest Japan

Five radiolarian zones, from the Upper Silurian to Middle Devonian, are discriminated from the tuffaceous successions of the Joryu and Nakahata Formations of the Yokokurayama Group of the Yokokurayama area and the Konomori area in the Kurosegawa Belt, Southwest Japan. The definition of the zones is based on the first appearance biohorizon of the characteristic species. The zones are the Pseudospongoprunum sagittatum, Futobari solidus, Trilonche (?) sp. A, Glanta fragilis and Protoholoeciscus hindea zones, in ascending order. The preliminary age assignments for the zones are discussed on the basis of the comparison with other previous documented faunas. The age determination of the formations suggests the presence of unconformities and the episodic sedimentation of the tuffaceous strata in the Yokokurayama Group.     

Latest Jurassic–earliest Cretaceous radiolarian fauna from the Xialu chert in the Yarlung Zangbo suture zone, southern Tibet: Comparison with coeval western Pacific radiolarian faunas and paleoceanographic implications

Abstract The Xialu chert radiolarian fauna is latest Jurassic–earliest Cretaceous in age (Pseudodictyomitra carpatica zone) and contains many taxa in common with coeval northern hemisphere middle‐latitude (temperate) radiolarian faunas represented by the Torinosu fauna in southwest Japan. Common elements include Eucyrtidiellum pyramis (Aita), Protunuma japonicus Matsuoka & Yao, Sethocapsa pseudouterculus Aita, Sethocapsa (?) subcrassitestata Aita, Archaeodictyomitra minoensis (Mizutani), Stichocapsa praepulchella Hori and Xitus gifuensis (Mizutani). The Xialu fauna is less similar to low‐latitude (tropical) assemblages represented by the Mariana fauna. For this reason, the Xialu fauna is regarded as representative of a southern hemisphere middle‐latitude (temperate) fauna. A mirror‐image bi‐temperate provincialism to the equator in radiolarian faunas is reconstructed for the Ceno‐Tethys and Pacific Ocean in latest Jurassic–earliest Cretaceous time.     

祁连山地震带小震活动增强指标提取与预报效能分析

总结2015年以来、2010年以来和1980年以来祁连山地震带活动增强指标，得到祁连山地震带5年、10年以及40年尺度的小震频度预报效能。祁连山地震带M_L2.0以上地震月频度持续增强的异常出现时间在3个月以上，异常出现后1~3个月，祁连山地震带及边邻地区发生5级以上地震以及青藏高原东北缘发生6级以上地震的概率较高。作为短期预报指标，祁连山地震带的地震活动增强对甘肃及边邻地区的地震预报工作具有重要的指示意义。     

Preliminary report on Lower Jurassic radiolaria of Gondwana origin from the Kawhia coast, New Zealand

Abstract Well-preserved radiolarians from the Newcastle Group in southwest Kawhia, New Zealand, constitute the first record of Lower Jurassic radiolarians from in situ deposits in high latitudes of the Southern Hemisphere on the margin of Gondwana. The radiolarians were extracted from carbonate nodules from five horizons in the Rewarewa Formation and the lower part of the Arawhero Formation, in the Murihiku Terrane. The radiolarian-bearing sequence, which lies within the upper part of the type section of the local Aratauran Stage, is roughly datable as Hettangian-Sinemurian from rare ammonite occurrences. The radiolarian assemblages consist, on average, of 80–90% spumellarians and 10–20% nassellarians. Spumellarians include species of the following genera: Archaeotriastrum, Crucella, Emiluvia (?) Homeoparo-riaella, Orbictilifomaa, Pantanellium, Paronaella (?), Pseudocrucella, PseIIdoheliodiscus, Spon-gostaurus and Spongotrochus. Nassellarians are composed of species of Ragotum, Bipedis, Droltus, Jams (?) Perispyridium (?) Raoultius, Riedelius, Saitoum and Thetis. From data of Lower Jurassic radiolarian faunas of Europe, North America and Japan, the New Zealand fauna shows stronger affinity with those of the European Tethys such as Turkey (e.g. De Wever 1982) and the Northern Alps (Kozur & Mostler 1990) than with faunas from other areas of the circum-Pacific. This connection between the European Tethyan and New Zealand faunas is not well explained by presently accepted continental reconstructions (Smith et al. 1994) for the Early Jurassic.     

Conditional Probability Approach of the Assessment of Tsunami Potential: Application in Three Tsunamigenic Regions of the Pacific Ocean

We develop stochastic approaches to determine the potential for tsunami generation from earthquakes by combining two interrelated time series, one for the earthquake events, and another for the tsunami events. Conditional probabilities for the occurrence of tsunamis as a function of time are calculated by assuming that the inter-arrival times of the past events are lognormally distributed and by taking into account the time of occurrence of the last event in the time series. An alternative approach is based on the total probabilitiy theorem. Then, the probability for the tsunami occurrence equals the product of the ratio, r (= tsunami generating earthquakes/total number of earthquakes) by the conditional probability for the occurrence of the next earthquake in the zone. The probabilities obtained by the total probability theorem are bounded upwards by the ratio r and, therefore, they are not comparable with the conditional probabilities. The two methods were successfully tested in three characteristic seismic zones of the Pacific Ocean: South America, Kuril-Kamchatka and Japan. For time intervals of about 20 years and over the probabilities exceed 0.50 in the three zones. It has been found that the results depend on the approach applied. In fact, the conditional probabilities of tsunami occurrence in Japan are slightly higher than in the South America region and in Kuril-Kamchatka they are clearly lower than in South America. Probabilities calculated by the total probability theorem are systematically higher in South America than in Japan while in Kuril-Kamchatka they are significantly lower than in Japan. The stochastic techniques tested in this paper are promising for the tsunami potential assessment in other tsunamigenic regions of the world.     

Multifractal measures of earthquakes in west Taiwan

The generalized fractal dimension for epicentral distribution of earthquakes in west Taiwan is measured. The entire area is first divided into two zones, i.e., north and south zones, after which the two zones are further separated into three subzones for the former and two for the latter. The logC _q (r) versus logr function, whereC _q (r) is the generalized correlation integral andr is the distance between two epicenters, shows that a linear relation between logC _q and logr exists in the range ofr smaller thanr _c . The value ofr _c is 25 km for the north zone, 40 km for the south and 12 km for the three north subzones. The valuesr _c =25 and 40 km are almost the smallest ones of the width of epicentral distributions of the north and south zones, respectively. The value ofr _c =12 km for the three north subzones is approximately the smallest size of the cluster of epicenters. For the plots of two south subzones, the pattern of data points does not bend in the range ofr in consideration, and, thus, there is not such a critical radius. TheD _q –q relations forq=0, 1, 2,..., 15 are constructed for the two zones and five subzones. Results show significant multifractality and a spatial variation in multifractality for epicentral distributions of earthquakes in west Taiwan.     

The Kellwasser events in the Upper Devonian Frasnian to Famennian transition in the Toc Tat Formation,northern Vietnam

Upper Devonian carbonates of the Toc Tat Formation in the Si Phai Pass area of Dong Van District, northern Vietnam were deposited in carbonate platform, slope, and basin environments. These carbonates yield abundant conodonts indicative of the Palmatolepis nasuta, Pa. linguiformis and Pa. triangularis zones, the Frasnian–Famennian stage boundary being identified by the first occurrence of Pa. triangularis. Two positive carbon isotope excursions are recognized, the lower excursion peaking in the interval of the lower to middle Pa. nasuta Zone, whilst the upper excursion peaks just above the local Frasnian–Famennian boundary. Based on the biostratigraphy, these excursions equate to the Lower and Upper Kellwasser events. Locally, tentaculitoid taxa (Nowakia, Styliolina, Homoctenus, and Metastyliolina?) are abundant in the interval of the Pa. nasuta Zone, but show a drastic decline in abundance before the Lower Kellwasser Event, and only two taxa survived into the Famennian.     

Probability forecast of earthquake magnitude in Chinese mainland before A．D． 2005

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Succession and global correlation of Late Tremadoc graptolite zones from South China

The Tremadocian is the first stage of the Ordovician System and is subdivided into two parts in general. The Upper Tremadocian, spanning a temporal interval of ca. 8 Ma, yields graptolite faunas crucial for biostratigraphic division and correlation in high resolution. Relatively complete successions of Upper Tremadoc graptolite zones have been proposed in Scandinavia, and North and South America. In South China, the coeval graptolite strata are widespread in deep water facies, but the successions of graptolite zones recognized so far are quite incomplete and thus very difficult to be correlated with those in other countries. In recent years, we have sampled bed by bed the Nanba section in the Yiyang area, Hunan Province and, below the Tetragraptus approximatus Zone, identified four Upper Tremadoc graptolite zones in descending order: the Hunnegraptus copiosus Zone, the Araneograptus murrayi Zone, the Aorograptus victoriae Zone and the Adelograptus tenellus Zone. To date, the Nanba section is the only section in China that presents a relatively complete and globally comparable succession of Upper Tremadoc graptolite zones. Therefore, this study not only confirms the existence of some Upper Tremadoc graptolite zones that were never found before in China, but also facilitates a highly resolved division and correlation for the Upper Tremadoc graptolite strata in China. Supported by National Natural Science Foundation of China (Grant No. 40472014)     

Mesozoic radiolarian faunas from the northwest Ilocos Region,Luzon, Philippines and their tectonic significance

Northwestern Ilocos Norte in Luzon, Philippines, exposes cherts, peridotite and a variety of metamorphic rocks including chlorite schist, quartzo‐feldspathic schist, muscovite schist and actinolite schist. These rocks are incorporated within a tectonic mélange, the Dos Hermanos Mélange, which is thrust onto the turbidite succession of the Eocene Bangui Formation and capped by the Upper Miocene Pasuquin Limestone. The radiolarian assemblages constrain the stratigraphic range of the cherts to the uppermost Jurassic to Lower Cretaceous. Stratigraphically important species include Eucyrtidiellum pyramis (Aita), Hiscocapsa acuta (Hull), Protunuma japonicus (Matsuoka & Yao), Archeodictyomitra montisserei (Squinabol), Hiscocapsa asseni (Tan), Cryptamphorella conara (Foreman) and Pseudodictyomitra carpatica (Lozyniak). The radiolarian biostratigraphic data provide evidence for the existence of a Mesozoic basinal source from which the cherts and associated rocks were derived. Crucial to determining the origin of these rocks is their distribution and resemblance with known mélange outcrops in Central Philippines. The mélange in the northwestern Ilocos region bears similarities in terms of age and composition with those noted in the western part of the Central Philippines, particularly in the islands of Romblon, Mindoro and Panay. The existence of tectonic mélanges in the Central Philippines has been attributed to the Early to Middle Miocene arc–continent collision. This event involved the Philippine Mobile Belt and the Palawan Microcontinental Block, a terrane that drifted from the southeastern margin of mainland Asia following the opening of the South China Sea. Such arc–continent collision event could also well explain the existence of a tectonic mélange in northwestern Luzon.     

Regularities in the time variations of seismic parameters and their implications for prediction of strong earthquakes in Greece

Time variations in the parameters of seismic activity in two regions in Greece, which are known to have different geodynamical conditions, are analyzed using the FastBEE algorithm suggested in (Papadopoulos and Baskoutas, 2009). The study is based on the data on weak earthquakes that occurred in two local regions. One region pertains to the zone dominated by intensive compression stress field, while another is located in the region of a relatively lower intensity extension stress field. It is shown that in the zone of compression the seismic parameters exhibit anomalous temporal behavior before strong earthquakes with Ms ≥ 5.7, whereas in the zones of extension, similar anomalies precede earthquakes with lower magnitudes of up to Ms ≥ 4.9. The most informative parameters for the purposes of predicting strong seismic events are the released seismic energy in the form logE ^2/3 and the slope of the frequency-magnitude dependence, b-value. The seismic activity in the region, expressed in terms of the logarithmic number of earthquakes, per unit time in some cases does not exhibit any particular pattern of behavior before strong earthquakes. In the time series of the studied parameters, four stages in the seismic process are clearly distinguished before strong earthquakes. Typically, a strong earthquake has a low probability to occur within the first two stages. Instead, this probability arises at stage III and attains its maximum at the end of this stage coinciding with the occurrence of the strong earthquake. We suggest these features of the time series to be used for the assessment of seismic hazard and for the real-time prediction of strong earthquakes. The time variations in the b-value are found to be correlated with the time variations inlogE ^2/3. This correlation is closely approximated by the power-law function. The parameters of this function depend on the geodynamical features of the region and characterize the intensity and the type of the regional tectonic stresses. The results of our study show that the FastBEE algorithm can be successfully applied for monitoring seismic hazard and predicting strong earthquakes.     

Historical seismicity and deformation rates in the Indian Peninsular Shield

Seismic strain rates for the entire Indian Peninsular Shield are estimatedfrom the available historical and recently observed seismicity data fromthe last 199 years (1800–1998). Typical strain rates ranging from10^-13 to 10^-8 per year have been calculated for differentregions of Peninsular India by using Anderson's (1979) method andanalysis. A correlation between the seismically deforming zones and highheat flow areas has been observed. The deformation zones are divided intotwo classes, with low and high deformation zones of Cratons and Mobilebelts with further sub-divisions. Seismo-tectonics of the SouthernPeninsular India is also discussed in the light of recent occurrence ofthe disastrous earthquakes of Killari (September 29, 1993) and Jabalpur(May 21, 1997).     

An unusual zone of seismic coupling in the Bonin arc: The 1972 Hachijo-Oki earthquakes and related seismicity

The 1972 February and December Hachijo-Oki earthquakes (M _s=7.3 and 7.4), in the northernmost part of the Izu-Bonin subduction zone, are the only major events (M _s>7.0) in the Bonin arc for the past 80 years. Relocation of the hypocenters, using one smaller event having a wellconstrained focal depth as a master event, shows that the depth of the February event is 10 km shallower than that of the December event. We have determined the rupture process for both events by minimizing the error in waveform between observed and synthetic seismograms. Although the number of available stations are limited, the depth range of the major energy release for the December event extends deeper than for the February one. The rupture propagated up-dip for both events. It is likely that the rupture zone of the two events overlapped, and that the December event ruptured the deeper part. This suggestion is consistent with the observation that the aftershock zones of both events overlap with that of the December event shifted landward. The waveforms of the December event have a smaller high frequency component than those of the February event, suggesting that the stress at the thrust zone became more uniform or reduced after the February event.No thrust type smaller event occurred near the rupture zone. Instead, theP-axes of smaller events are parallel to the dip of the slab and theirT-axes dip to the southwest. Focal depths of these events estimated byP-wave forward modeling are generally between 40–50 km and located beneath the thrust zone. We thus interpret them as the events within the Pacific slab near the zone ruptured by the two major events. The stress concentration around the rupture zone of the major events is suggested to have triggered these slab events. After the occurrence of the large events, the slab events are concentrated near the deeper portion of the rupture zone. These events may have been caused by the loading of the down-dip compressional stress near the down-dip end of the rupture zone due to the rupture. The occurrence of the doublet of large earthquakes and a number of down-dip compressional events beneath their rupture zones in a shallow portion of the subducting slab indicates an unusual zone of seismic coupling in the Bonin arc, most of which is seismically quiescent.     

U–Pb zircon age from the radiolarian‐bearing Hitoegane Formation in the Hida Gaien Belt,Japan

The dating of radiolarian biostratigraphic zones from the Silurian to Devonian is only partially understood. Dating the zircons in radiolarian‐bearing tuffaceous rocks has enabled us to ascribe practical ages to the radiolarian zones. To extend knowledge in this area, radiometric dating of magmatic zircons within the radiolarian‐bearing Hitoegane Formation, Japan, was undertaken. The Hitoegane Formation is mainly composed of alternating beds of tuffaceous sandstones, tuffaceous mudstones and felsic tuff. The felsic tuff and tuffaceous mudstone yield well‐preserved radiolarian fossils. Zircon grains showing a U–Pb laser ablation–inductively coupled plasma–mass spectrometry age of 426.6 ± 3.7 Ma were collected from four horizons of the Hitoegane Formation, which is the boundary between the Pseudospongoprunum tauversi to Futobari solidus–Zadrappolus tenuis radiolarian assemblage zones. This fact strongly suggests that the boundary of these assemblage zones is around the Ludlowian to Pridolian. The last occurrence of F. solidus is considered to be Pragian based on the reinterpretation of a U–Pb sensitive high mass‐resolution ion microprobe (SHRIMP) zircon age of 408.9 ± 7.6 Ma for a felsic tuff of the Kurosegawa belt, Southwest Japan. Thus the F. solidus–Z. tenuis assemblage can be assigned to the Ludlowian or Pridolian to Pragian. The present data also contribute to establishing overall stratigraphy of the Paleozoic rocks of the Fukuji–Hitoegane area. According to the Ordovician to Carboniferous stratigraphy in this area, Ordovician to Silurian volcanism was gradually reduced to change the sedimentary environment into a tropical lagoon in the early Devonian. And the quiet Carboniferous environment was subsequently interrupted, throwing it once more into the volcanic conditions in the Middle Permian.     

Shear localisation in upper mantle peridotites

Upper mantle peridotite bodies at the earth's surface contain relict structures and microstructures which provide direct information on the role and the mechanisms of shear localisation in the upper mantle. Deformation which occurred at high temperatures (T>950±50°C) is relatively homogeneous within domains ranging in scale from a few kilometres to a few tens of kilometres. Below 950±50°C strain is localised into centimetre to several hundred metre wide shear zones which commonly contain hydrated mylonitic peridotites. The microstructures developed in the peridotites suggest there is a correlation between the occurrence of shear localisation and the occurrence of strain softening and brittle deformation processes. The most important strain softening processes are inferred to be structural and reaction induced softening. Structural softening processes include dynamic recrystallisation and strain-induced transitions from dislocation creep to some form of grain-size-sensitive (GSS) creep. Reaction induced softening is related to the formation of fine grained polyphase reaction products which deform by GSS creep and the formation of weak sheet silicates such as phlogopite, chlorite, talc and antigorite. From experimental studies these softening processes and brittle deformation processes are inferred to occur mainly at temperatures less than about 910±160°C. This temperature range is inferred to be a significant rheological transition in the upper mantle. Below 910±160°C deformation during orogenesis may be accommodated by an anastomosing network of hydrated mylonitic shear zones with a distinct, perhaps weak, rheology. At higher temperatures strain is accommodated in much wider deformation zones.On the scale of the lithosphere the degree of localisation may be different to that determined at the scale of the periodotite massif. An anastomosing network of hundred metre wide mylonitic shear zones forming 0.05–0.3 by volume fraction of the mantle lithosphere atT<950°C could accommodate inhomogeneous or homogeneous bulk deformation depending on the spatial distribution and ordering of the mylonite zones. The higher temperature deformation at deeper levels in the mantle could be markedly inhomogeneous being concentrated in shear zones with widths in the range of 2–20 km, alternatively these zones may widen significantly during deformation, resulting in a decrease in the degree of localisation with increasing bulk strain.     

Chronological and paleoceanographic constraints of Miocene to Pliocene ‘mud sea’ in the Ryukyu Islands (southwestern Japan) based on calcareous nannofossil assemblages

The Cenozoic sedimentary succession in Okinawa‐jima, including the upper Miocene to Pleistocene siliciclastic deposits (Shimajiri Group) and the Pleistocene reef to shelf deposits (Ryukyu Group), suggests a drastic paleoceanographic change from a ‘mud sea’ to a ‘coral sea.’ To delineate the paleoceanographic evolution of the mud sea, we quantified the stratigraphic distribution of the calcareous nannofossil assemblages from the Shimajiri Group in a 2119.49 m‐deep well (Nanjo R1 Exploratory Well) drilled in southern Okinawa‐jima (Ryukyu Islands, southwestern Japan). Four late Miocene and Pliocene datum planes were found in the studied interval: the first occurrence of Amaurolithus spp. (7.42 Ma), the last occurrence of Discoaster quinqueramus (5.59 Ma), the first occurrence of Ceratolithus rugosus (5.12 Ma), and the last occurrence of Reticulofenestra pseudoumbilicus (3.70 Ma). The calcareous nannofossil assemblages from the Tomigusuku Formation and the lower part of the Yonabaru Formation are characterized by a lower total number of coccoliths and abundant Sphenolithus abies that is associated, at times, with common Discoaster spp. Overall, these suggest the existence of oligotrophic conditions between 5.3 and >8.3 Ma. The total number of coccoliths increased and small Reticulofenestra spp. became more common in the middle part of the Yonabaru Formation, suggesting that eutrophic conditions were present between 3.5 and 5.3 Ma. The rare occurrence of calcareous nannofossils in the upper part of the Yonabaru Formation indicates a return to oligotrophic conditions at 3.5 Ma. Micropaleontological evidence suggests that these oceanographic changes were likely caused by local tectonic movement (shallowing of the sedimentary basin in which the Shimajiri Group was deposited).     

Explanatory analysis of the relationship between atmospheric circulation and occurrence of flood‐generating events in a coastal city

The aim of this study is to enhance the understanding of the occurrence of flood‐generating events in urban areas by analysing the relationship between large‐scale atmospheric circulation and extreme precipitation events, extreme sea water level events and their simultaneous occurrence, respectively. To describe the atmospheric circulation, we used the Lamb circulation type (LCT) classification and re‐grouped it into Lamb circulation classes (LCC). The daily LCCs/LCTs were connected with rare precipitation and water‐level events in Aarhus, a Danish coastal city. Westerly and cyclonic LCCs (W, C, SW and NW) showed a significantly high occurrence of extreme precipitation. Similarly, for extreme water‐level events westerly LCCs (W and SW) showed a significantly high occurrence. Significantly low occurrence of extreme precipitation and water‐level events was obtained in easterly LCCs (NE, E and SE). For concurrent events, significantly high occurrence was obtained in LCC W. We assessed the change in LCC occurrence frequency in the future based on two regional climate models (RCMs). The projections indicate that the westerly directions in LCCs are expected to increase in the future. Consequently, simultaneous occurrence of extreme water level and precipitation events is expected to increase in the future as a result of change in LCC frequencies. The RCM projections for LCC frequencies are uncertain because the representation of current LCCs is poor; a large number of days cannot be classified and the frequencies of the days that can be classified differ from the observed time series. Copyright © 2015 John Wiley & Sons, Ltd.     

Palinspastic restorations for the south Tien Shan mountains and Tajik depression based on paleomagnetic data

In terms of plate tectonic concepts, horizontal movement are responsible for the formation of fold belts, and modern structures are interpreted by the position of the belt relative to the zones of plate collision. Paleomagnetic data allow the reconstruction of the former positions of these zones relative to a geographic grid, their pre-deformation patterns being important to the solution of problems in fold belt tectonics (Van der Voo et al., 1980; Khramov et al., 1982).Fold structures within the south-western spurs of the Tien Shan Mountains and the intermontane basins separating them were the first to be studied (Rzhevsky, 1966). Paleomagnetic studies aimed at understanding the tectonic setting of the region have been undertaken during the ensuing years and also cover adjacent areas of Central Asia (Khramov et al., 1982).In this paper an attempt is made to summarize some paleomagnetic results, produced palinspastic reconstructions of the region and produce a framework to help understand the formation of one of the crucial parts of the Alpine-Himalayan belt.     

Variability in the vertical hyporheic water exchange affected by hydraulic conductivity and river morphology at a natural confluent meander bend

River confluences and their associated tributaries are key morphodynamic nodes that play important roles in controlling hydraulic geometry and hyporheic water exchange in fluvial networks. However, the existing knowledge regarding hyporheic water exchange associated with river confluence morphology is relatively scarce. On January 14 and 15, 2016, the general hydraulic and morphological characteristics of the confluent meander bend (CMB) between the Juehe River and the Haohe River in the southern region of Xi'an City, Shaanxi Province, China, were investigated. The patterns and magnitudes of vertical hyporheic water exchange (VHWE) were estimated based on a one‐dimensional heat steady‐state model, whereas the sediment vertical hydraulic conductivity (K_v) was calculated via in situ permeameter tests. The results demonstrated that 6 hydrodynamic zones and their extensions were observed at the CMB during the test period. These zones were likely controlled by the obtuse junction angle and low momentum flux ratio, influencing the sediment grain size distribution of the CMB. The VHWE patterns at the test site during the test period mostly showed upwelling flow dominated by regional groundwater discharging into the river. The occurrence of longitudinal downwelling and upwelling patterns along the meander bend at the CMB was likely subjected to the comprehensive influences of the local sinuosity of the meander bend and regional groundwater discharge and finally formed regional and local flow paths. Additionally, in dominated upwelling areas, the change in VHWE magnitudes was nearly consistent with that in K_v values, and higher values of both variables generally occurred in erosional zones near the thalweg paths of the CMB, which were mostly made up of sand and gravel. This was potentially caused by the erosional and depositional processes subjected to confluence morphology. Furthermore, lower K_v values observed in downwelling areas at the CMB were attributed to sediment clogging caused by local downwelling flow. The confluence morphology and sediment K_v are thus likely the driving factors that cause local variations in the VHWE of fluvial systems.     

Seismic Zonation of the Delhi Region for Bedrock Ground Motion

An endeavor is made to compute peak ground horizontal accelerations at bedrock level in the Delhi region due to the seismogenic sources present around Delhi. The entire area is divided into six seismogenic sources for which seismic hazard analysis is carried out using the complete and extreme part of the seismicity data. Maximum likelihood estimates of hazard parameters viz., seismic activity rate , b value and maximum probable earthquake M _max are made for each zone. The return periods and the probabilities of occurrence of various magnitudes for return periods of 50, 100 and 1000 years are also computed for each zone. The peak ground acceleration (PGA) values for 20% exceedance in 50 years are then computed for the Delhi region from each zone. The maximum PGA value considering all the zones is 0.34 g, which is due to the Mathura fault zone. The seismogenic zones V and VI, i.e., Mathura fault zone and the Sohna fault zone are observed to be contributing maximum PGA values in the Delhi region governing the isoacceleration contours computed for the region. The seismic zonation map for the PGA values at the bedrock level is obtained for the Delhi region. This can be used directly as input for the microzonation of ground motion at the surface by incorporating the local site conditions.