Thick Alluvium Research Articles

Origin of Land Subsidence and Earth Fissuring, Northeast Phoenix, Arizona

Differential subsidence over a buried bedrock hill caused by rapid water-level decline resulted in a 400-ft (120 m) long earth fissure in a northeast Phoenix construction site in January, 1980. This is the first occurrence in the Paradise Valley basin, and the first within the city of Phoenix. Local water levels have declined more than 300 ft (90 m) accompanied by 3.44 ft (1.05 m) of measured subsidence, with indirect evidence for 5 ft (1.5 m). The depth to ground water is as much as 580 ft in the area. The maximum subsidence rate measured was 0.44 ft. (0.13 m) annually. Water levels began dropping in the mid-19509s, and subsidence began a decade later after 100 to 150 ft (30 to 45 m) of decline in water level. The subsidence bowl has grown about 2 mi 2 (5 km 2 ) annually, first mostly westward, and more recently north and east, with further expansion expected. More than 9 ft (3 m) of subsidence is possible. Gravity survey results suggest the fissure is associated with a bedrock hill buried at 150 ft (45 m) on a large pediment. Measured differential subsidence, after Assuring, occurred in a pattern similar to the inferred subsurface bedrock configuration, indicating that the fissure was coincident with surficial horizontal tensile maxima above the crest of the buried hill. Maximum annual strain and accumulated tensile strain at the time of Assuring were calculated at 0.01 percent and 0.06 percent, respectively. These data suggest future reactivation of the filled-in fissure, and on the basis of gravity measurements, probable lengthening of the fissure. Finite element analysis indicates maximum surficial tensile stress of 3,400 psf (1.4 kg/cm 2 ) and strain of 0.19 percent when Assuring occurred. The large pediment that underlies most of the study area is divided into a shallow inner part [less than 500 ft (150 m) deep] of moderate relief; and a deeper, outer part gently sloping northeastward from 500 to 1,000 ft (150 to 300 m). The pediment is separated from thick alluvial deposits toward the center of the valley by a major NW-SE normal fault. This subsurface configuration controls the spatial pattern of land subsidence, water-level decline, and future Assuring. Fissures may be localized in three geologic settings: 1) buried bedrock hills, 2) the hinge-line of subsiding areas, and 3) buried faults.

Investigation of a coarse alluvial foundation for an embankment dam

Investigation of the coarse alluvial foundation for the Pichi Picun Leufu embankment dam is described and evaluated. Direct and indirect investigation methods are compared and an assessment is made of their relative adequacy in order to gain a realistic understanding of foundation conditions. Indirect methods—dynamic cone penetration testing and shear wave velocity measurement—calibrated by comparative testing in a test embankment, have been found to provide a satisfactory means of evaluating the density of thick alluvial deposits below the water table. Relationships of relative density, penetration resistance, and shear wave velocity are discussed. Dynamic penetration resistance normalized for effective overburden pressure appears to be the more sensitive indicator of changes in material density. Key words: coarse alluvium, relative density, dynamic penetration, shear wave velocity, test embankment, overburden pressure.

A Graphics System for Seismic Response Mapping

The area around St. Louis, Missouri, is one of the largest population centers of the United States. It also is located within 200 mi (322 km) of one of the most seismically active regions of the United States, the New Madrid fault zone. This region was the location of one of the greatest sequences of earthquakes in North American history, the New Madrid earthquakes of 1811 and 1812. In addition to the proximity of this area to an active seismic region, other geologic factors exist that add to the potential for property damage and loss of life from earthquakes. The urban expansion has extended onto thick lacustrine and alluvial deposits along the Mississippi and Missouri rivers. These deposits tend to be of the type which are highly susceptible to ground failure by liquefaction. The objective of this paper is to present a seismic hazards mapping procedure based on the geology, seismicity, dynamic response of the soil deposits, and state-of-the-art engineering analyses for the St. Louis region. The mapping procedure considers the relative potential for slope failure, liquefaction, and damage to structures by ground motion from a given earthquake. The procedure is demonstrated by computer-generated earthquake hazards maps of a portion of the Creve Coeur Quadrangle, St. Louis County, Missouri.

Erosion‐sedimentation in a Closed Drainage Basin in Northwest Indiana

AbstractA closed drainage basin representing a catchment for eroded sediment was studied to determine the amount of erosion since cultivation began, and to determine the spatial relationships of the erosion‐sedimentation process that had occurred during 145 yr of agriculture. Post‐settlement alluvium (PSA) thickness was easily determined in the field as light‐colored mineral soil overlying highly decomposed (sapric) organics in the depression. A detailed field study of the PSA, other geologic sediments, loess, and the original till surface in the watershed demonstrated a reduction in the original relief. The mass of PSA served as a measure of the amount of soil eroded from peripheral slopes. The long term average soil loss was > 26 Mg ha−1 yr−1, which represented an average removal of over 24 cm of soil from the entire watershed in 145 yr. The maximum slope in the watershed was 5%. The loess thickness on the surrounding slopes was used as an indication of the spatial variation of erosion processes. Summit positions and convex slope shapes having divergent runoff had the most erosion while concave shapes with convergent runoff exhibited more sedimentation. These results are essentially opposite to those predicted by the Universal Soil Loss Equation (USLE). Accurate prediction models in the future should consider the dynamic aspects of erosion‐sedimentation on landscapes.

Seismic Data Acquisition in San Juan Volcanic Field: ABSTRACT

The 1982, 1983, and 1984 Colorado School of Mines Geophysics Department summer field camp data acquisition was in the San Juan volcanic field between Monte Vista, Colorado, and the Continental Divide 30 mi west of Monte Vista. The objectives included (1) determining which techniques were most successful at retrieving data through volcanic layers, and (2) trying to see if there was seismic evidence for Cretaceous and older sediments beneath the volcanics. Both of these objectives met with success. Seven seismic lines (approximately 40 mi) were acquired in this area. Field tests were also conducted along these lines. Each of the three data sets (1982, 1983, and 1984) were acquired using two Vibroseis trucks, 110-ft shot and group intervals, off-end spreads, 48 groups per shot, and 12 to 24 fold. Number of sweeps, drive level, sweep frequencies, source and group arrays, and minimum and maximum offsets were changed for each data set. These changes were beneficial in some respects and harmful in others. Lengthening the group array helped cancel the ground roll but also attenuated higher frequency data. Increasing the low frequency cutoff helped cut out ground roll but resulted in less interpretable data character. Increasing minimum offsets helped to cut out ground roll but also re ulted in loss of some shallow reflections. A beneficial acquisition parameter for this area was the reduced energy level input into the ground. Variations in near-surface geology also caused data quality differences. The best data were acquired where a fairly consistent thickness of alluvium covered the volcanic rocks. End_of_Article - Last_Page 1042------------

Geomorphic Development of the Alluvial Plain along the Lower Nagdong River, Korea

The Nagdong River Basin occuping the area of 24, 000km2 with 525km long trunk stream is located in the southeastern part of the Korean Peninsula. The alluvial plain along the lower Nagdong is divided into two areas, i. e. the down-reaches basin and the river-mouth delta.This study intends to clarify geomorphic characteristics and geomorphic development of this plain in relation to post-glacial sea-level change. The investigation is made up of micro-landform classification, stratigraphic analysis, and restoration of depositional environment.The main findings are as follows:1) There are buried valleys below the 50-70m thick alluvium in th delta, and below the 15-10m thick one at Woegwan located about 210km upstream from the river mouth.2) The alluvium of the delta is classified into the following six different layers in ascending order; Basal Gravel (BG), Lower Silt-Clay (LC), Middle Sand (MS), Middle Silt-Clay (MC), Upper Sand (US) and Upper Clay (UC). The LC and MC are considered to be the bottom-set bed deposited in the transgression phase. The MS and US are considered to be the foreset or topset bed formed in the regression phase.3) The above mentioned sequence of alluvial deposits shows that there are two large sealevel fluctuations in the post-glacial time in this plain as demonstrated in the plains of Central Japan (Ikeda, 1964).4) In the longitudinal profile, the LC and MC show a wedge-shape structure which is sharp upstream. These layers were traced up to 50km (LC) and 150km (MC) from the river mouth.5) In the cross-section of down-reaches basin, silty clay lenses are recognized on the both sides of main stream and are identified as back marsh deposits which formed in submerged environment during the transgression.6) Geomorphic development of this alluvial plain are summarized as follows:a) The down-reaches of Nagdong River was drowned in the postglacial transgression. This drowned valley was consequently filled continuously with stream deposits supplied from the neighbouring mountain sides and with flood deposits provided from the main Nagdong River sides. The area of water surface was gradually decreased. The back marshes such as Upo, Samolpo etc., are the latest remnants of water surface.b) The delta plain formed on the river mouth is made up of three different geomorphic units, that is, the main delta, the lower delta and the marginal marsh. In the bay, the main delta was formed by bifurication of main stream resulting in the formation of interdistributary islands. By contrast in the bay mouth which is affected by open sea, the lower delta consisting of beach ridge, swale, and barrier islands has been developed. The development of main delta provided the enclosure of water surface and resulted in the formation of marginal marsh.

Fluvial Surfaces of the Saline River Valley, Western Kansas

The Saline River valley in Ellis County contains surfaces shaped by both erosional and depositional fluvial processes. The surfaces are described and illustrated in terms of form, position within the valley, and relative height. Most of the valley is composed of graded slopes (also referred to as pediments) and three distinct alluvial terrace surfaces. Typical floodplain features are absent on the relatively narrow active floodplain. A recent phase of stream rejuvenation and down-cutting is suggested. The valley of the Saline River in Ellis County (see Fig. 1) contains several distinct and areally extensive features whose surfaces, as viewed in crossvalley profiles, are essentially planar or slightly concave. Most of these surfaces are underlain with alluvial deposits (commonly exceeding several tens of feet in thickness) and, therefore, are clearly alluvial terraces or floodplain. Between the highest alluvial surface and the bedrock bluffs which mark the distal edge of the valley proper are remnants of smooth, concaveupward slopes that flatten streamward and merge imperceptibly with the adjacent terrace surface. This paper describes the various fluvial surfaces of the Saline River valley and discusses their significance in terms of the geomorphic development of the valley. The surfaces are described in terms of form, position, and relative height within the valley. These data were extracted from topographic maps and from the interpretation of aerial photographs. Field observations yielded supplementary topographic information and revealed the general nature of the underlying deposits. Well logs filed by oil well drillers define the alluvial thickness but rarely have a stratigraphic resolution fine enough to differentiate among the various alluvial deposits. Figure 2 illustrates, in plan and profile, the fluvial surfaces of the valley in Sections 3, 4, 9, 10, 15, and 16, Township 11 South, Range 17 West. All of the surfaces introduced above (which, of course, do not occur continuously along the valley) are well represented in this six square-mile area. The valley margins are quite irregular in plan view, particularly where minor streams, through headward extension, have eroded the upland. Larger trib

EVOLUÇÃO PALEOGEOGRÁFICA E ESTRUTURAL DA PORÇÃO CENTRAL DA BACIA BAMBUÍ, NO NORTE DO ESTADO DE MINAS GERAIS

Three large and distinct lithological sets were deposited at the center of the Bambuí Basin, during the final phase of the Pre-Cambrian period, respectively characterized by exclusive carbonated (limestones and dolostones), clastic and pelitic (siltstones and mudstones) and clastic or carbonated (siltstones and black limestones) natures. In previous works, such facies have been considered as in ill-defined lateral equivalence, strictly over the region which is now occupied by São Francisco River, under its thick alluvial deposits which masks all the details of contact. The present work establishes a characterization of the paleogeographical domains for each of the litho-stratigraphic units, which negates the suggested distribution of the facies by evidencing the complex relations exibited by them. In addition, the stratigraphic columns, proposed for the Paraopeba Formation, in the same region, cannot survive within the present model.

Marine Terraces and Quaternary Tectonism, Northwest Baja California, Mexico

Deformed marine terraces provide excellent measures of Quaternary tectonism along 400 km of the Pacific coast of Baja California between Ensenada and Punta Blanca. The nature and magnitude of deformation are well expressed by the present elevation of the marine limit, of Upper Pliocene or Lower Pleistocene age, which has been upwarped to 345m, 357m, and at least 195m in three separate localities, while occurring at lower levels elsewhere. Multiple terraces are found below this marine limit where appreciable uplift has occurred. Where relative subsidence has prevailed, fewer broader terraces or thick alluvial and eolian deposits occur. Terraces are further dislocated by NW-SE strike-slip faulting and by normal faults that trend NE-SW across the coast. Folding and faulting are less significant on the younger terraces than on the older features, and negligible for the Sangamonian terrace, except close to major faults. Crustal movements revealed by these terraces, and by similar features in southern Californi...

Anomalous distribution of seismic intensities due to the descending Philippine Sea plate beneath the southern Kanto district, Japan.

An examination has been made of the distribution of seismic intensities by the earthquakes which occurred in the uppermost mantle beneath the Kanto district, Japan, during the period between 1949 and 1978. Anomalously high seismic intensities were observed on the eastern side of the Izu Peninsula (Ajiro (AJI) and Oshima (OSH)) for the earthquakes at depths between 60 and 70km beneath northern and central Tokyo Bay. High seismic intensities were also observed along the western shore of Tokyo Bay (Tokyo (TOK) and Yokohama (YOK)) and on the eastern side of the Izu Peninsula (Ajiro and Oshima) for the earthquakes in the depth range from 60 to 80km beneath northern and central Chiba. The high seismic intensities observed at Tokyo and Yokohama must have been due to an amplification of ground motion by the thick alluvial deposits along the western shore of Tokyo Bay. It is in our opinion that these anomalously high seismic intensities observed at Ajiro and Oshima are caused by the practically unattenuated transmission of seismic waves through the descending Philippine Sea plate that dips northeastwards from the Sagami trough beneath the southern Kanto district. The existence of this plate had been suggested from seismicity and earthquake mechanism studies, but not confirmed from seismic wave transmission. High seismic intensities on the eastern side of the Izu Peninsula were also observed from the earthquakes at depths between 70 and 80km beneath southern Ibaraki. The earthquakes in the depth range from 30 to 60km beneath southwestern Ibaraki show normal concentric distribution of seismic intensities. These characteristic distributions of seismic intensities can be explained by the locations of earthquakes and the geometry of the high-Q plates.A comment is made on a possible systematic error of epicenter locations of the historically earlier earthquakes along the western shore of Tokyo Bay (Tokyo-Yokohama area).

Evaluation of the relation between near-surface geological units and ground response in the vicinity of Long Beach, California

abstract Simulataneous recordings of Nevada Test Site nuclear events were made at sites underlain by alluvium in the Long Beach, California, area and at sites underlain by rock in the Palos Verdes and Pasadena areas. These data show peak-ground-velocity alluvium-to-rock ratios as large as 7 and spectral ratios as high as 11 in the period band from 0.2 to 6 sec. Comparison of the low-strain nuclear-explosion data and the San Fernando earthquake strong-motion data at three sites indicates that the alluvium-to-rock spectral ratios derived from the nuclear explosions are similar to those derived from the earthquake. Significant trends exist in the short-period data, indicating higher ground response at sites underlain at the near-surface by materials that have high void ratios and lower ground response with increasing thickness of Quaternary deposits. These results suggest that the short-period response is primarily controlled both by near-surface low-velocity layers and by attenuation in the Quaternary sediments. Comparison of the data of this study with data collected in other areas indicates that the long-period response increase with either increasing depth to basement or with alluvium thickness, when this thickness is greater than 400 m. From previous theoretical studies and these results, ground response in the long-period band is related to those underlying geological structures and major velocity contrasts that control the development of surface waves.

Microseisms in geothermal exploration—studies in Grass Valley, Nevada

Frequency(f)‐wavenumber(k) spectra of seismic noise in the bands 1 ⩽ f ⩽ 10 Hz in frequency and |k| ⩽ 35.7 cycles/km in wavenumber, measured at several places in Grass Valley, Nevada, exhibit numerous features which can be correlated with variations in surface geology and sources associated with hot spring activity. Exploration techniques for geothermal reservoirs, based upon the spatial distribution of the amplitude and frequency characteristics of short‐period seismic noise, are applied and evaluated in a field program at this potential geothermal area. A detailed investigation of the spatial and temporal characteristics of the noise field was made to guide subsequent data acquisition and processing. Contour maps of normalized noise level derived from judiciously sampled data are dominated by the hot spring noise source and the generally high noise levels outlining the regions of thick alluvium. Major faults are evident when they produce a shallow lateral contrast in rock properties. Conventional seismic noise mapping techniques cannot differentiate noise anomalies due to buried seismic sources from those due to shallow geologic effects. The noise radiating from a deep reservoir ought to be evident as body waves of high‐phase velocity with time‐invariant source azimuth. A small two‐dimensional (2-D) array was placed at 16 locations in the region to map propagation parameters. The f‐k spectra reveal shallow local sources, but no evidence for a significant body wave component in the noise field was found. With proper data sampling, array processing provides a powerful method for mapping the horizontal component of the vector wavenumber of the noise field. This information, along with the accurate velocity structure, will allow ray tracing to locate a source region of radiating microseisms. In Grass Valley, and probably in most areas of sedimentary cover, the 2–10 Hz microseismic field is predominantly fundamental‐mode Rayleigh waves controlled by the very shallow structure.

Recent seismic activity in Delhi and neighbourhood

In ordert o assess the seismic status of existing faults burried under thickalluvial deposits in the plains around Delhi, a tot al of 937 recorded shocks have been analysed. The spatial and temporal distibut ions of earthquakes and strain release pat terns have been discussed with reference1 the positions and trends of the existing fault pat tern s. The value of slope coefficient h was found to decrease before and increase just after the major events.

Chronology and evolution of landforms during the late quaternary in the Tokachi Plain and adjacent areas, Hokkaido, Japan

The succession of various geomorphological processes associated with climatic fluctuations in the late Quaternary and their effects on the landform of the Tokachi Plain are discussed using chronological data on glacial landforms, marine terraces, river terraces, fossil periglacial phenomena and mass movements on the mountain slopes, together with analytical data on the terrace deposits, present river deposits and slope deposits. Three major stages are recognized in the landform evolution after about 60 000 years B.P.. The division of stages is based on the chronology of the fluvial and marine terraces. The stage of the KoI terrace (60 000 – 35 000 or 30 000 years B.P.) is marked by the maximum extent of cirques in the Hidaka Range, vigorous periglacial mass movements on the mountain slopes, and by conspicuous fluvial accumulation in the regions of alluvial fan and upper reaches of each river. This fluvial accumulation seems to have occurred under glacial and periglacial morphogenetic environments. The stage of the KoII — KoIII terraces (35 000 or 30 000 – 10 000 years B.P.) is characterized by the restriction of the glaciers in the Hidaka Range, active solifluction processes on the mountain slopes, remarkable periglacial phenomena, especially sand dune development and involutions, on the terrace surfaces of the Tokachi Plain and a deep incision due to depression in sea level in the lower reaches of the Tokachi River. The stage of the KoIV terrace (10 000 years B.P. — Present) is characterized by wholly different events from the former stages, such as vigorous incision of rivers into the alluvial fans and mountainous regions, accumulation of thick alluvium in the lower reaches of the Tokachi River, and recovery of vegetation on the mountain slopes. Aufgrund von Untersuchungen der Chronologie des vergletscherten Gebietes, der marinen und fluvialen Terrassen, der fossilen Periglazialerscheinungen einschließlich periglazialer Massenbewegung auf den Hängen, sowie aufgrund entsprechender sedimentlogischen Untersuchungen wurde die Abfolge der verschiedenen geomorphologischen Prozesse, die von den Klimaschwankungen während des Jungquartärs gesteuert wurden, sowie Auswirkungen auf die Reliefentwicklung der Tokachi-Ebene diskutiert. Es können drei Hauptabschnitte in der geomorphologischen Entwicklung der letzten 60 000 Jahre unterschieden werden. Diese Abschnitte sind aufgrund der Chronologie der fluvialen Terrassen ausgeschieden worden. Der KoI-Abschnitt (60 000 bis 35 000 oder 30 000 vor heute) ist durch den größten Vorstoß der Kargletscher im Hidaka-Gebirge, durch periglaziale Massenbewegungen auf den Hängen und durch mächtige Schotterakkumulationen auf den Schwemmfächern und in den Flußtälern gekennzeichnet. Der KoII — KoIII-Abschnitt (35 000 oder 30 000 bis 10 000 vor heute) ist durch den Rückzug der Kargletscher im Hidaka-Gebirge, durch starke Solifluktionsaktivität auf den Hängen, durch periglaziale Erscheinungen, besonders Sanddünen und Kryoturbationen auf den Terrassenoberflächen der Tokachi-Ebene und durch die Tieferosion im unteren Laufbereich des Tokachi, die von der Meerregression verursacht wurde, gekennzeichnet. Der KoIV-Abschnitt (10 000 — Gegenwart) ist gegenüber den vorhergegangenen Abschnitten durch vollkommen unterschiedliche geomorphologische Prozesse sowie ausgeprägte Tieferosion auf den Schwemmfächern und in den Flußtälern, Akkumulation im unteren Laufbereich des Tokachi und durch die Wiederbesiedlung des Gebirges mit einer geschlossenen Vegetationsdecke gekennzeichnet.

Possibility of a major earthquake in the tokai district, Japan and its pre-estimated seismotectonic effects

Crustal deformations, tsunamis and seismic intensity are pre-estimated for a large hypothetical earthquake, which it is feared may occur in the Tokai district along the Nankai trough. The long-term seismic quiescence since 1854, as well as the high rate of the present crustal movements in the district, form the principal evidence for the risk of the approaching catastrophe. The location and the mode of faulting in this earthquake are hypothesized in reference to the source mechanisms of the recent and historical earthquakes there. The fault parameters thus assumed are as follows: dip direction: N30°W; dip angle: 25°; fault dimension : 100 km × 70 km; dislocation: 4 m (reverse dip-slip: 3.8 m; right-lateral strike-slip: 1.3 m). The following are the principal conclusions: (a) the eastern part of the epicentral region including the Point Omaezaki will rise up about 100 cm, whereas the western part covering Ise and Mikawa bays will subside about 10–30 cm; (b) the coast extending from Omaezaki to the Shima peninsula will receive tsunami waves as high as 3 m in maximum, which may be locally amplified by the factor 2 or more on the rias coast along the Shima peninsula; (c) the Tokai coastal region with thick alluvium layers may suffer seismic damages as severe as those experienced in the 1854 Ansei I earthquake.

東京都区内における木造家屋の震害予測のための実態調査と地震応答計算について

This paper describes an investigation into the actual conditions and distributions of wooden houses on the all districts in Tokyo as to their uses, number of stories, lapse after construction and the ratio of effective wall length to building area. And also the author pursues their process into collapse and measures their vibrational damage by the earthquake response analysis which is considered the above mentioned conditions of them. Calculated damage ratios show good agreement with actual damage of wooden houses due to Kanto Earthquake 1923 in the downtown districts which have comparatively thick alluvium.

The Dunedin earthquake, 9 April, 1974

The earthquake of 9 April, 1974 was the strongest experienced in the Dunedin area in historic times. It was centred at sea about 10 km south of the city and had a magnitude of 5.0. The felt intensity reached MMVII in the St. Clair area, where a ground acceleration of 0.27 g was recorded.
 Variations in felt intensity were determined from a survey of grocery stores. The intensity decreased rapidly away from a maximum on the alluvial ground of the southern suburbs and correlated strongly with the underlying rock type.
 The number of claims received by the Earthquake and War Damage Commission was extraordinarily large for an earthquake of this magnitude. Damage, generally of a rather minor nature, was reported from all parts of the city, but was greatly concentrated in the South Dunedin - St. Clair area. About half of the 3000 claims received included chimney damage.
 The effects of the earthquake highlight the need to assess the safety of public buildings in Dunedin, particularly those sited on areas of thick alluvium.

THE LANDFORM EVOLUTION OF THE TOKACHI PLAIN

The Tokachi Plain is located on the eastern side of the Hidaka Range, the back-bone of Hokkaido, where a number of glacial landforms are well preserved (Fig.1). It has long been pointed out that the Tokachi Plain is one of the most important region for the Quaternary research in Japan. Widely developed alluvial fans at the foot of the Hidaka Range, an alluvial plain in the lowest reach of the Tokachi River and marine terraces along the Pacific coast are no less stimulative for geomorphologists than the glacial topographies in the Range. In this paper, the authors discussed the landform evolution of the Tokachi Plain in order to clarify (1) the relation between the construction of alluvial fans in the Plain and the glaciatin in the Range, and (2) the relation between fluvial terraces and marine terraces indicating sea level changes in the late Quaternary. The surfaces of these terraces are covered with tephra layers, to which the authors refer as the Tokachi Loam (Fig.2). Key beds of characteristic pumice or scoria layers in the Tokachi Loam and continuity of terrace surfaces lead to a classification of the fluvial and marine terra ces (Table 1, Fig.3) and their chronological arrangement (Fig. 8). Of the marine terraces, the O II surface consisting of thick marine deposits seems to have been built under the heighest sea level in the Eemian Interglacial age. The 0 IV surface shows a slight transgression at about 60, 000 years P. P.. Consequently, the fluvial surfaces younger than the 0 IV surface are included in the Warm Glacial and Postglacial ages. From the view point of the landform evolution, at least three phases are recognized in these ages as described below. (1) 60, 000 30, 000 Tears B. P. Valley filling and expansion of alluvial fans were conspicuous in the Plain; the Ko I filltop terrace surface was formed just before the fall of Spfa (Sh.ikotsu Pumice Fall Deposits). (2) 30, 000.10, 000 years B. P. Neither deposition nor downcutting were remarkable in the area of alluvial fans. The alluvial fans of the Ko II and Ko gj surfaces were constructed as strath terrace surfaces in rather limited areas compared to the former Ko I surface. Whereas in the lowest reach of the Tokachi River, deep incision, which was caused by a regression reaching about 1.20 m below sea level at the maximum, resulted in a steeper gradient of the longitudinal profile of the Ko II surface (Fig.7). (3) 10, 000 years B. P.-Present In the area of alluvial fans vigorous incision reaching 20 to 50 m in depth took place ; alluvial fans and river terraces of the Ko I, II and f surfaces were cut down to form many strath terraces of the Ko IV surfaces. While in the lowest reach, of the Tokachi River, the Postglacial transgression caused deposition of thick alluvium to bury the surfaces of Ko I-Ko II (Fig.7). The glacial landforms in the Hidaka Range, consisting of cirques and moraines, are either younger and fresh or older and dissected. The distribution of the older ones is much extensive than the younger. Contrary to the generally held view that the older landforms are correlated to the Kiss Glacial in age, the authors are of opinion that they are rather correlated to the early stadial of Wurm Glacial age. The moraines and out-wash deposits of the older stadial (Poroshiri Stadial) are probably correlated to the fill gravels of the Ko I surface. And those of the younger stadial (Tottabetsu Stadial) are probably correlated to the deposits of Ko II surface. It can be concluded that the la.ndform evolution of the Tokachi Plain has been controlled by the sea level changes in the lowest reach of the Tokachi River and by the climatic changes in the alluvial fan areas or the upper reaches.

Local distribution of strong earthquake ground motions

abstract Twenty ground stations distributed over a 40-square-mile area in Pasadena recorded strong ground shaking during the San Fernando earthquake of February 9, 1971. Relative responses at 10 of these same stations as measured for small earthquakes by standard Wood-Anderson torsion seismometers are available for comparison from a study made by Gutenberg in the 1950's. Frequency spectra of strong ground motions as calculated for four sites having time-recording accelerographs assist in the interpretation of seismoscope results at the other stations. Attempts to correlate local distributions with known features of local geology such as thickness of alluvium, distance from known faults, etc., indicate that no single feature plays a dominant role in the resulting patterns. The implications of such complicated distributions for the preparation of seismic risk maps are discussed, and it is concluded that it would not be possible in the present state of knowledge to assess meaningful variations in the seismic risk throughout the Pasadena area.

Correlation of Marine and Nonmarine Strata with Example from Devonian of New York State

Correlation between marine and nonmarine strata is particularly difficult because of the lack of fossils that span both realms of sedimentation. However, certain changes in the marine realm way produce sedimentologic effects in the nonmarine realm. Such a cause-and effect relation provides a rationale for correlation. Recent work in New York has shown that two limestones (Tully and Portland Point) are equivalent to transgressive marine clastic tongues which intertongue with contemporaneous nonmarine Catskill redbed sequence. On the basis of regional structure and thickness trends, it is estimated that nonmarine strata equivalent to these limestone bodies should be found at 1,400- and 900-ft elevations, respectively, in the bed of Kaaterskill Creek at the Catskill front. The writer suggests that the transgressions caused an increased rate of alluviation on the Catskill alluvial plain and that the equivalent beds in nonmarine sections should be anomalously thick overbank alluvial deposits. Examination of stratigraphic sections in the area of the Catskill front shows the presence of extremely thick (more than 100 ft) overbank alluvium in the position predicted for the Tully, and a thicker-than-normal section (62 ft) at one locality in the position predicted for the Portland Point equivalent. These beds are considered to be correlative with the marine transgressive strata on the west.