geology geochronology and tectonic setting of the jorullo volcano region michoacan mexico abstract the jorullo monogenetic volcano erupted 250 years ago at the southern border of the trans mexican volcanic belt tmvb an area that records a long history of magmatic and tectonic activity the oldest rocks that crop out in the area are early oligocene 32 7 0 2 ma dioritic to granitic 60 72 wt sio2 plutons intruded by younger to contemporaneous 30 3 0 1 and 33 3 0 7 ma aplitic 76 78 wt sio2 dikes and mineralized veins volcanic rocks related to these intrusives form a thick sequence exposed in cliffs from the base of which an altered andesite 58 wt sio2 was collected the nearby epithermal cu mineralization of the inguaran mining area to the southeast is also related to this tertiary volcanic episode the oldest expression of the tmvb in this area is represented by pliocene 3 2 2 4 ma basaltic andesite to andesite 53 63 wt sio2 lavas with pyroxene olivine forming extensive mesas eroded mounds and thick elongate flows that were unconformably deposited on top of the oligocene rocks their emplacement was followed by erosion approximating a rate of 100 m ma over the past 3 ma this led to the formation of an inverted topography reflecting the higher resistance to erosion of these lavas that were originally deposited in valleys and today constitute prominent mesas during the last 1 ma at least twenty six monogenetic scoria cones formed in the study area erupting about 10 2 km3 of lava and pyroclastics dominantly composed of olivine and pyroxene bearing andesites 61 vol dre lesser basaltic andesites 30 vol dre and a minority of olivine rich basalts 10 vol dre these eruptive products include the k rich basaltic trachyandesites of cerro la pilita a scoria and lava cone located close to jorullo the 27 ka san hilario and esmeralda lavas which are located 13 km southeast of jorullo are the southernmost eruptive products of the tmvb and also the youngest volcanoes after jorullo in this area mapping of main faults and scoria cone alignments on regional and local scales reveals that the ascent of dikes feeding quaternary eruptions in the jorullo area was controlled by west northwest and west southwest basement structures northeast oriented subduction related horizontal compressional stress probably associated with crustal fractures and a major northwest trending seismically active fault zone that passes near paricutin and jorullo

modeling substorm current systems using conductivity distributions inferred from de auroral images images of auroral emissions observed with dynamics explorer 1 de 1 are used to calculate ionospheric conductivities over the polar region the combination of ground based magnetometer data and the inferred conductivities enables us to estimate on a global scale the distributions of ionospheric electric fields and currents and field aligned currents as well as the joule heating production rate with a time resolution of 12 min although our inference of the conductivity distribution requires further improvements the following conclusions may be drawn from this work 1 the westward electrojet is in general collocated with the region of high auroral luminosity while the region of relatively low luminosity in the evening sector is collocated with the eastward electrojet 2 the upward field aligned currents exist in the brightest auroral region on the poleward side of the evening auroral oval and on the equatorward side of the morning oval however the magnitudes of these upward currents are not in proportion to the auroral luminosities suggesting that the characteristic energies of precipitating electrons carrying the upward currents and generating the auroral luminosities may be different 3 a significant amount of ionospheric currents can flow in regions where there are no bright auroral emissions an example of this effect is found over the poleward half of the westward electrojet in the morning sector where the electric field is the main contributor to the ionospheric currents 4 the distribution of calculated field aligned currents displays many localized structures which characterize the development of the substorm current system previous satellite observations may represent gross time averages of such complicated distributions

a 4000 year lacustrine record of environmental change in the southern maya lowlands peten guatemala a 4000 yr sediment core record from lake salpeten guatemala provides evidence for maya induced forest clearance and consequent soil erosion between 1700 cal yr b c and 850 cal yr a d radiocarbon ages of wood seeds and charcoal support an age depth model with average errors of 110 cal yr relatively low carbonate 18o values between 1300 and 400 cal yr b c coincide with pollen evidence for forest loss consistent with increased surface and groundwater flow to the lake minimum 18o values between 400 cal yr b c and 150 cal yr a d suggest a high lake level as do 14c dated aquatic gastropods as much as 7 5 m above the present lake stage high lake levels resulted from reduced evaporation to precipitation ratios increased hydrologic input caused by anthropogenic deforestation or both the preclassic abandonment 150 a d and early classic late classic boundary 550 a d are marked by relatively high 18o values indicating reduced lake levels oxygen isotope composition increased further coincident with the terminal classic maya demographic decline between 800 and 900 a d this period of high 18o may have been caused by the greater aridity that has been documented in northern yucatan lakes or by decreased hydrologic input to the lake as a consequence of forest recovery reduced soil erosion after 850 cal yr a d coincided with the terminal classic maya demographic decline and permitted forest recovery and resumption of organic sedimentation

surface vector mapping of magnetic anomalies over the moon using kaguya and lunar prospector observations we have provided preliminary global maps of three components of the lunar magnetic anomaly on the surface applying the surface vector mapping svm method the data used in the present study consist of about 5 million observations of the lunar magnetic field at 10 45 km altitudes by kaguya and lunar prospector the lunar magnetic anomalies were mapped at 0 2 equi distance points on the surface by the svm method showing the highest intensity of 718 nt in the crisium antipodal region overall features on the svm maps indicate that elongating magnetic anomalies are likely to be dominant on the moon except for the young large basins with the impact demagnetization remarkable demagnetization features suggested by previous studies are also recognized at hertzsprung and kolorev craters on the farside these features indicate that demagnetized areas extend to about 1 2 radii of the basins craters there are well isolated central magnetic anomalies at four craters leibnitz aitken jules verne and grimaldi craters their magnetic poles through the dipole source approximation suggest occurrence of the polar wander prior to 3 3 3 5 ga when compared with high albedo markings at several magnetic anomalies such as the reiner gamma anomalies three dimensional structures of the magnetic field on near the surface are well correlated with high albedo areas these results indicate that the global svm maps are useful for the study of the lunar magnetic anomalies in comparison with various geological and geophysical data

14c and 40ar 39ar radiometric dating and geologic setting of young lavas of rancho seco and mazcuta volcanoes hosting archaeological sites at the margins of the patzcuaro and zacapu lake basins central michoacan mexico abstract geologic mapping of two neighbouring areas totalling 770 km2 centred around the rancho seco and mazcuta monogenetic scoria cones and situated between the patzcuaro and zacapu lake basins in the michoacan guanajuato volcanic field central portion of the trans mexican volcanic belt allowed the recognition of 62 quaternary monogenetic volcanic structures which include cinder cones with associated lava flows domes and small to medium sized shields 40ar 39ar and 14c radiometric dating petrography and whole rock chemical analyses of volcanic products provide a stratigraphic framework and insight into different eruptive styles and erupted volumes 45 km3 of calc alkaline magma pliocene to holocene monogenetic activity has been frequent in this region forming structures which are generally aligned along an ene wsw direction associated to the morelia cuitzeo acambay normal fault system the young rancho seco and mazcuta volcanoes are of particular interest because their distal lava flows host the pre hispanic archaeological urban centres of angamuco and cortijo viejo respectively the rancho seco scoria cone was radiocarbon dated at 27 845 445 425 yr bp and emitted at least six andesitic lava flows which were emplaced toward the sw lake patzcuaro covering an area of 21 3 km2 with a volume of 0 64 km3 the mazcuta scoria cone dated at 7970 135 yr bp produced five basaltic andesite andesite lava flows toward the nw lake zacapu where they cover an area of 28 85 km2 with a volume of 0 57 km3 the recently studied archaeological site of angamuco became an important urban centre during the rise of the tarascan empire in the post classic period 900 1521 ce while the cortijo viejo site remains largely unexplored but its occupation might fall within the same period although the young lava flows on which these sites are built seem inhospitable and barren with a rugged topography and rocky substrate unfit for agriculture early inhabitants adapted and modified its surface according to their needs hence these archaeological sites exemplify how a seemingly hostile landscape was ingeniously modified to establish population centres with patterns similar to those observed on lava flows elsewhere

neotectonics in central mexico regional neotectonic activity in central mexico was mapped through analysis of eleven landsat thematic mapper images the study area stretches from mexico city on the east to the gulf of california on the west between 17 and 21 n latitude fault scarps of plio quaternary age define several large scale tectonic features within the mexican volcanic belt dominated by rifting transtension and shear with probable sinistral components three large crustal blocks south of the mexican volcanic belt are separated from the north american plate and from each other by zones of neotectonic activity that express the relative motions between the adjacent blocks a simple vector diagram for plates and crustal blocks in central mexico has been constructed using information from the literature combined with the orientations of fault zones as mapped in this study the relative motion between the blocks varies from about 2 5 to 8 mm year 1 which is comparable to motions of crustal blocks in areas of active rifting in other parts of the world in the mexican volcanic belt there is a clear relationship between volcanism and neotectonic activity fault zones that traverse nearly the entire region have the same location and orientation as the volcanic belt this may indicate that deformation within the crust of the overriding slab plays a significant role in determining the unusual orientation of the mexican volcanic belt relative to the trench the ultimate factor controlling the location of plio quaternary volcanism and tectonism in central mexico may be large zones of crustal weakness formed during major mesozoic and cenozoic tectonic events

successive collapses of the el estribo volcanic complex in the patzcuaro lake michoacan mexico abstract the el estribo volcanic complex is located in the north central part of michoacan state mexico within the michoacan guanajuato volcanic field it consists of a 126 kr shield volcano crowned by a cinder cone separated by a paleosol dated at 28 360 170 bp the shield volcano has been cut by the e w normal patzcuaro fault that exposes 200 m of piled up lavas flows our field reconstruction suggests that two collapses have been originated from this fault two debris avalanche deposits with hummocky topography are exposed between this fault and the southern shore of the patzcuaro lake the basal debris avalanche deposit bdad covers lacustrine sediments and is covered by a paleosol that at 28 110 720 yr bp yielding a minimum age for the event it had a maximum run out of 3 2 km with a h l of 0 0062 the upper debris avalanche deposit udad is overlain by a paleosol dated at 14 110 60 yr bp that yields a minimum age of the event it had a maximum run out of 2 3 km with a h l of 0 0086 no pyroclastic deposits have been found in association with these debris avalanches and the shield volcano rocks show signs of intense hydrothermal alteration or abundant clay minerals for which we assume that failure was triggered by seismic tectonic activity the older debris avalanche was more mobile because it moved on water and on top of water saturated sediments deforming them and likely originating a tsunami across the lake instead the younger debris avalanche moved across the previous rugged hummocky topography of the basal avalanche resulting in a more restricted dispersion these collapse events of el estribo the morphology of the scarp and historic and modern seismicity indicate that a future failure represents a serious threat to the surrounding communities of the patzcuaro lake consequently some preventive measurements as seismic and deformation rate monitoring are necessary today five villages with circa 1500 inhabitants live upon the mass waste deposits

the great mexican earthquake of 19 june 1858 expected ground motions and damage in mexico city from a similar future event abstract the description of the great earthquake of 19 june 1858 is unusual damage and high intensities were reported both in the state of michoacan and in mexico city although a coastal epicenter for this earthquake cannot be ruled out the reports agree better with an intermediate depth about 50 km normal faulting event in the subducted cocos plate a careful examination of the reports of this event and other normal faulting events below the mexican altiplano suggests that a likely location is 18 0 n 100 8 w near the epicenter of the 6 june 1964 m 7 3 h 55 km event this location is 220 km sw of the city the magnitude of the earthquake is estimated to be about 7 7 we synthesize expected ground motions in cu a hill zone site in the city from an event similar to that of 1858 using records from the 23 may 1994 earthquake 18 0 n 100 6 w h 50 km m 5 7 as an empirical green9s function and stress parameter of 50 160 and 300 bar the expected peak horizontal acceleration in cu of 160 bar is about 30 gals similar acceleration was recorded in cu during the 1985 michoacan earthquake m 8 0 we compute expected ground motions at many sites in mexico city using empirical transfer functions and random vibration theory and compare these motions and the expected damage in the city with those from the 1985 michoacan earthquake results show that the overall expected damage during the postulated earthquake is and 1 of that during the michoacan earthquake for 160 and 300 bar respectively a greater percentage of low rise construction which constitute about 80 of the total in the city will be damaged during the postulated earthquake than during the michoacan earthquake the expected ground motions for 50 bar are smaller at all periods than those from the michoacan earthquake as the present building code for mexico city contemplates coastal earthquakes of magnitude greater than 8 0 the case of 50 bar is not of interest in this article this preliminary study suggests a need for a more careful evaluation of expected ground motion in the valley of mexico from the postulated earthquake and its impact on the current design spectra of the city

the importance of earthquake induced landslides to long term slope erosion and slope failure hazards in seismically active regions abstract this paper describes a general method for determining the amount of earthquake induced landsliding that occurs in a seismically active region over time this determination can be used as a quantitative measure of the long term hazard from seismically triggered landslides as well as a measure of the importance of this process to regional slope erosion rates and landscape evolution the method uses data from historical earthquakes to relate total volume of landslide material dislodged by an earthquake to the magnitude m and seismic moment m0 of the earthquake from worldwide data a linear regression relation between landslide volume v and m0 is determined as v m0 1018 9 0 13 where v is measured in m3 and m0 is in dyn cm to determine the amount of earthquake generated landsliding over time this relation is combined with data on seismic moment release for a particular region which may be derived from either earthquake history or fault slip data the form of the m0 v relation allows the rate of production of earthquake induced landslides over time to be determined from total rate of seismic moment release without regard to the distribution of individual events thus simplifying and generalizing the determination application of the method to twelve seismically active regions with areas ranging from 13 275 to 2 308 000 km2 shows that erosion rates from earthquake induced landslides vary significantly from region to region of the regions studied the highest rates were determined for the island of hawaii new zealand western new guinea and the san francisco bay region of california significantly lower rates were determined for iran tibet the sierra nevada great basin region of california and central japan for the time period from 715 ad to the present intermediate rates were determined for peru southern california onshore california turkey and central japan for the time period from 1586 ad to the present to determine the relative long term importance of seismically triggered landslides these erosion rates are compared to erosion rates calculated for other slope processes and to rates calculated from fluvial sediment discharge comparisons with other slope processes indicate that earthquake induced landslides are the predominant agents of slope erosion on the island of hawaii in the san francisco bay region and in western new guinea for hawaii the san francisco bay region and sierra nevada great basin region of california the erosion rates calculated for earthquake induced landslides also exceed the regional erosion rates calculated from fluvial sediment discharge

el estribo volcanic complex evolution from a shield volcano to a cinder cone patzcuaro lake michoacan mexico abstract el estribo volcanic complex evc is located in the northern part of the michoacan guanajuato volcanic field within the trans mexican volcanic belt tmvb el estribo is located at the southern edge of the e w patzcuaro fault that belongs to the patzcuaro jaracuaro graben a western extension of the e w morelia acambay fault system stratigraphy geochronology chemistry and mineral assemblages suggest that the volcanic complex was constructed in two periods separated by a 100 ka volcanic hiatus a emission of lava flows that constructed a shield volcano between 126 ka and b mixed phreatomagmatic to strombolian activity that formed a cinder cone 28 ka the magmas that fed these monogenetic volcanoes were able to use the same feeding system the cinder cone itself was constructed by strombolian fallouts and remobilized scoria beds followed by an erosion period and by a mixed phreatomagmatic to magmatic phase strombolian fallouts ending with lava flows soft sedimentary deformation of beds and impact sags cross bedding as well as pitting and hydrothermal cracks found in particles support the phreatomagmatic phase the erupted magmas through time ejected basaltic andesitic lava flows 56 21 58 88 sio 2 that built the shield volcano and then basaltic andesitic scoria 57 65 59 05 sio 2 that constructed the cinder cone although they used the same feeding system the geochemical data and the mineral chemistry of the magmas indicate that the shield volcano and the cinder cone were fed by different magma batches erupted thousands of years apart therefore the location of el estribo volcanic complex along an e w fault that has generated two sector collapses of the shield volcano to the north may be directly linked to this complex redistribution of the magmatic paths to the surface our findings show that magmatic feeding systems within monogenetic volcanic fields could be long lived questioning the classic view of the monogenetic nature of their volcanoes and yielding information about the potential volcanic risk of these settings usually considered risk free

ancient igneous intrusions and early expansion of the moon revealed by grail gravity gradiometry the earliest history of the moon is poorly preserved in the surface geologic record due to the high flux of impactors but aspects of that history may be preserved in subsurface structures application of gravity gradiometry to observations by the gravity recovery and interior laboratory grail mission results in the identification of a population of linear gravity anomalies with lengths of hundreds of kilometers inversion of the gravity anomalies indicates elongated positive density anomalies that are interpreted to be ancient vertical tabular intrusions or dikes formed by magmatism in combination with extension of the lithosphere crosscutting relationships support a pre nectarian to nectarian age preceding the end of the heavy bombardment of the moon the distribution orientation and dimensions of the intrusions indicate a globally isotropic extensional stress state arising from an increase in the moon s radius by 0 6 to 4 9 kilometers early in lunar history consistent with predictions of thermal models

limnologic history of lago de patzcuaro michoacan mexico for the past 48 000 years impacts of climate and man abstract lago de patzcuaro lies at an elevation of 2035 m 19 36 n 101 39 w on the west part of the volcanic meseta central of mexico about 50 km east southeast of morelia pollen diatom and geochemical records from a 15 m core taken in 6 m of water continuously track vegetation and limnological changes in the patzcuaro basin for the past 48 ky calendar years pine oak and alder pollen dominate both the wisconsin and holocene vegetation record and indicate that this region did not witness strongly arid climates during that time before the holocene juniperus type and artemisia pollen document cooler climates of more effective moisture at least seasonally isoetes characterizes the full and late glacial interval 25 13 ka and implies along with the diatoms aulacoseira and stephanodiscus cool deep freshwater conditions at lago de patzcuaro the freshest and deepest lacustrine phase in the lake occurred 38 to 25 ka during this time lago de patzcuaro may have drained into the lerma river system between 30 and 10 ka diatom species that bloom in the winter and early spring imply moisture during those seasons evaluation of contemporaneous marine and terrestrial records west and east of lago de patzcuaro suggests that this moisture probably originated from westerly storm tracks shifted south by the laurentide ice sheet after 10 ka lago de patzcuaro became shallower and more eutrophic rooted aquatic plants prospered under a climate regime of negative hydrologic budgets increased seasonality and moisture arriving during the summer as it does today the lake became alkaline enough by the mid holocene to deposit ostracode rich marls at the core site for the first time in the past 48 ky indigenous agriculture in the patzcuaro drainage and around the lake appears about 4 ka with the appearance of zea and chenopodiineae pollen iron and potassium track increased soil erosion and planktic diatoms cyclostephanos record nutrients flushed into the lake from the drainage basin

long and short term change in the patzcuaro basin central mexico abstract data are presented from four new cores from the patzcuaro basin in the volcanic highlands of central mexico which provide new insights into climate change and human impact over the last 23 000 cal yr 19 000 14c yr bp the cores have been analysed for a range of proxies including mineral magnetic properties loss on ignition diatoms and stable isotope composition 18o and 13c high lake levels are recorded in the late pleistocene and early holocene with a probable shift from winter precipitation from the pacific in the late pleistocene to the modern summer regime in the early holocene gradual drying and increased climatic variability are indicated from the early holocene but particularly since 4000 cal bp consistent with southward displacement of the itcz the changing chemical composition and depth of the lake led to the accumulation of ostracod layers the timing of the late holocene dry intervals corresponds to global periods of rapid change driven by bond and or solar cycles by combining a range of proxies we have been able to identify climatic change even within a period of significant human disturbance the use of multiple cores indicates that a coherent climatic signal is recorded even in a basin subject to tectonic disturbance this study also provides new data to support the interpretation of major human impact on the basin in both the pre and post hispanic periods refuting continued suggestions that basin wide erosion occurred only after the spanish conquest a new model of sediment un mixing has been applied to identify different source materials contributing to deposition

origin of strong lunar magnetic anomalies further mapping and examinations of lroc imagery in regions antipodal to young large impact basins work at the university of arizona was supported under grant nnx12aj03g from the nasa lunar advanced science and exploration research laser program

prehistoric earthquake deformations near masada dead sea graben earthquake inducedfluidizations and suspensions of lake sediments associated with syndepositionalfaults formapaleoseismicrecordinthedeadseagraben theassociation offluidized beds with surface faulting supports the recognition of mixed layers as reliable earthquake indicators and provides a tool for the study of very long term 70 kar seismicity along the dead sea transform the faults compose a fault zone that offsets laminated sediments of the late pleistocene lake lisan they exhibit displacements of as much as 2 m layers of massive mixtures of laminated fragments are interpreted as disturbed beds each formed by an earthquake the undisturbed laminated layers between these mixed layers represent the interseismic interval a typical vertical slip of about 0 5 m per event is separated by several hundred years of quiescence the fault zone lies within the dead sea graben 2 km east of masada where archaeology and historical accounts indicate repeated strong earthquake damage the distribution of strikes in the fault zone resembles that of the faults exposed in and around the graben including the seismogenic ones the excellent exposures over hundreds of metres allow an unprecedented temporal and spatial resolution of slip events on faults

sedimentary record of the 1872 earthquake and tsunami at owens lake southeast california abstract in 1872 a magnitude 7 5 7 7 earthquake vertically offset the owens valley fault by more than a meter an eyewitness reported a large wave on the surface of owens lake presumably initiated by the earthquake physical evidence of this event is found in cores and trenches from owens lake including soft sediment deformation and fault offsets a graded pebbly sand truncates these features possibly over most of the lake floor reflecting the tsunami wave confirmation of the timing of the event is provided by abnormally high lead concentrations in the sediment immediately above and below these proposed earthquake deposits derived from lead smelting plants that operated near the eastern lake margin from 1869 1876 the bottom velocity in the deepest part of the lake needed to transport the coarsest grain sizes in the graded pebbly sand provides an estimate of the minimum initial tsunami wave height at 37 cm this is less than the wave height calculated from long wave numerical models about 55 cm using average fault displacement during the earthquake two other graded sand deposits associated with soft sediment deformation in the owens lake record are less than 3000 years old and are interpreted as evidence of older earthquake and tsunami events offsets of the owens valley fault elsewhere in the valley indicate that at least two additional large earthquakes occurred during the holocene which is consistent with our observations in this lacustrine record

lake level change climate and the impact of natural events the role of seismic and volcanic events in the formation of the lake patzcuaro basin michoacan mexico in central mexico lake level change is commonly used as a proxy for climatic fluctuation lacustrine sequences are not stable units however and have been dramatically impacted by processes related to the evolution of the mexican volcanic belt mvb and the fragmentation of the southern part of the north american plate including volcanism tectonic action landslides and human activity one notable example is the lake patzcuaro basin mexico which has one of the most intensively studied paleoenvironmental records in latin america geologic processes have altered the lacustrine sequence in the southwest portion of the lake basin during the last 48 000 years these include volcanic activity major uplift landslides and related tsunamis and earthquakes this new record has important implications for interpretations of climatic events in central mexico during the pleistocene and the impact these may have had on human settlement in the region

52 000 years of environmental history in zacapu basin michoacan mexico the magnetic record abstract mineral magnetic and total organic carbon toc measurements were performed on a 10 9 m long core from zacapu basin central mexico the sequence dated by ams 14 c spans the last ca 52 kyr curie temperature measurements low temperature susceptibility and low temperature remanence indicate that the magnetic fraction is characterized by oxidized titanomagnetites with variable ti content low s 300 ratios reflect the existence of high coercivity iron oxide phases these characteristics are considered to reflect the presence of goethite rather than hematite formed in relatively wet organic conditions where soil forming processes were intense comparison between magnetic and toc results suggests that the sediments record relatively humid conditions before 35 kyr bp and a later trend towards drier conditions a probable hiatus is recorded before 25 kyr and relatively dry conditions after this time that persisted throughout the late glacial maximum and mid holocene at 4 8 kyr these results contrast with previous observations of deep lake phases in the neighboring lake patzcuaro considered to be result of increased precipitation between 34 and 21 kyr bp

estimation of the tectonic slip rate from quaternary lacustrine facies within the intraplate albacete province se of spain abstract the quaternary lacustrine basin of cordovilla cb represents one of the most active tectonic areas of the prebetic zone albacete se of spain the quaternary sedimentary deposits of this basin are mainly endoreic lacustrine carbonate and alluvial deposits developed in a semi arid climate pleistocene present the basin is a nw se elongated graben bounded by a major right lateral oblique fault the pozohondo fault this fault trends nw se with an approximate trace of 55 km and is composed of various segments which are identified by fault scarps in order to establish the slip rate of the most active segment of the pozohondo fault called the cordovilla segment we carried out a detailed study of the affected quaternary lacustrine deposits we found that the lacustrine facies could be related to episodic moderate paleoearthquakes the slip rate is calculated to be 0 05 and 0 09 mm yr using radiometric dating for the vertical offsets of the lacustrine facies a trenching study at the northern part of the cordovilla segment revealed two events caused by paleoearthquakes with the most recent expressed as an oblique fault off setting a poorly developed soil the magnitude of the last event was greater than 6 using various empirical relationships for the fault displacement and the surface length rupture we estimate episodic activity across the cordovilla segment to be characterized by moderate sized paleoearthquakes m6 which is in agreement with the tectonic context of an intraplate zone of the iberian plate

magnetic signature of the lunar south pole aitken basin character origin and age 1 a new magnetic map of the moon based on lunar prospector magnetometer observations sheds light on the origin of the south pole aitken basin spa the largest and oldest of the recognized lunar basins a set of wnw trending linear to arcuate magnetic features evident in both the radial and scalar observations covers much of a 1000 km wide region centered on the nw portion of spa the source bodies are not at the surface because the magnetic features show no first order correspondence to any surface topographic or structural feature patchy mare basalts of possible late imbrian age are emplaced within spa and are inferred to have been emplaced through dikes directly from mantle sources we infer that the magnetic features represent dike swarms that served as feeders for these mare basalts as evident from the location of the thomson mare ingenii van de graaff and leeuwenhoek mare basalts on the two largest magnetic features in the region modeling suggests that the dike zone is between 25 and 50 km wide at the surface and dike magnetization contrasts are in the range of 0 2 a m we theorize that the basaltic dikes were emplaced in the lunar crust when a long lived dynamo was active based on pressure temperature and stress conditions prevalent in the lunar crust dikes are expected to be a dominantly subsurface phenomenon consistent with the observations reported here

paleoecological studies at lake patzcuaro on the west central mexican plateau and at chalco in the basin of mexico abstract a 1520 cm sediment core from lake patzcuaro michoacan mexico is 44 000 yr old at the base all parts of the core have abundant pollen of pinus pine alnus alder and quercus oak with frequent abies fir the interval dated from 44 000 to 11 000 yr ago has a homogeneous flora characterized by abundant juniperus juniper pollen and frequent artemisia sagebrush it is believed to represent an appreciably drier and colder climate than at present the holocene at lake patzcuaro is characterized by a moderate increase in pinus pollen and the loss of juniperus pollen as the modern type of climate succeeded alnus was abundant until about 5000 yr ago its abrupt decrease with the first appearance of herbaceous weed pollen may reflect the cutting of lake shore and stream course alder communities for agricultural purposes or it may simply reflect a drying tendency in the climate pollen of zea corn appears at lake patzcuaro along with low peaks of chenopod and grass pollen at 3500 yr b p apparently recording a human population large enough to modify the natural environment as well as the beginning of agriculture a rich aquatic flora in this phase suggests eutrophication of the lake by slope erosion in the most recent period corn is absent from the sediments perhaps reflecting a change in agricultural practices the environment changes at lake patzcuaro are similar to and correlate with those in the cuenca de mexico where diatom stratigraphy from the chalco basin indicates fluctuations in lake levels and lake chemistry in response to variations in available moisture before 10 000 yr ago climates there were cool and dry and the chalco basin was occupied by a shallow freshwater marsh that drained north to lake texcoco where saline water accumulated by evaporation increases in effective moisture and possible melting of glaciers during the holocene caused lake levels to rise throughout the cuenca de mexico and lake texcoco flooded the chalco basin with brackish water after 5000 yr ago such flooding decreased and shallow freshwater ponds and marshes were restored in the chalco basin this environmental change coincides with the appearance of zea pollen and suggests cultural control of lake levels and salinity

the springs of lake patzcuaro chemistry salt balance and implications for the water balance of the lake abstract lake patzcuaro the center of the ancient tarascan civilization located in the mexican altiplano west of the city of morelia has neither river input nor outflow the relatively constant lake salinity over the past centuries indicates the lake is in chemical steady state springs of the south shore constitute the primary visible input to the lake so influx and discharge must be via sub lacustrine ground water the authors report on the chemistry and stable isotope composition of the springs deeming them representative of ground water input the springs are dominated by ca mg and na whereas the lake is dominated by na combining these results with previously published precipitation rainfall measurements on the lake the authors calculate the chemical evolution from spring water to lake water and also calculate a salt balance of the ground water lake system comparing cl and 18o compositions in the springs and lake water indicates that 75 80 of the spring water is lost evaporatively during evolution toward lake composition during evaporation ca and mg are lost from the water by carbonate precipitation each liter of spring water discharging into the lake precipitates about 18 7 mg of caco3 salt balance calculations indicate that ground water input to the lake is 85 9 106 m3 a and ground water discharge from the lake is 23 0 106 m3 a thus the discharge is about 27 of the input with the rest balanced by evaporation a calculation of time to reach steady state ab initio indicates that the cl concentration of the present day lake would be reached in about 150 a

estimation of the paleoepicentral area from the spatial gradient of deformation in lacustrine seismites tierras blancas basin mexico abstract a new methodology is introduced to estimate the most probable epicentral area for a paleoearthquake interpreted from seismites within a quaternary basin seismites were described from various detailed stratigraphic logs within the tierras blancas basin tbb a pleistocene lacustrine area located in the central part of the trans mexican volcanic belt tmvb the lacustrine landscape evolution of tbb has been determined by the recent fault activity of the morelia acambay fault system mafs the tbb is bounded by active normal faults striking e w this fault activity has generated soft sediment deformation structures sand silt and gravel dikes pillows diapirs and decametric slumps disturbing the sedimentary infilling from these seismites and their stratigraphic spatial correlation five strong moderate paleoearthquakes e1 e5 have been established in the basin the spatial distribution of these seismites exhibits a gradient of perturbation defined by the intensity of deformation three different degrees of intensity deformation ddi are associated with the liquefacted grain size sediments i silt liquefaction ii silt and sand liquefaction and iii silt sand and gravel liquefaction this spatial gradient indicates an increase of the energy involved from the seismic activity related with the proximity of the source mapping the boundaries among these zones of deformation and interpolation of each ddi limit for paleoearthquake e4 was used to construct paleoseismic isolines of deformation as a potential indicator of the most probable paleoepicentral zone a 1 5 km 2 elongate zone oriented nnw sse is the potential paleoepicentral area associated with paleoearthquake e4 within the tbb

timing and characteristics of the latest mare eruption on the moon unraveling the timing and duration of mare volcanism on the moon is essential for understanding its thermal evolution the end of mare volcanism is poorly constrained because mare basalts are incompletely sampled in this study employing selene kaguya high resolution images we performed new crater size frequency measurements for 49 young mare units 3 0 ga in the procellarum kreep terrane pkt in which the latest magma eruption of the moon occurred mare volcanism in this region continued until 1 5 ga suggesting that volcanic activity in this region ceased 1 0 ga after the magma eruption had globally ceased 2 5 3 0 ga volcanic activity may have peaked 1 8 2 2 ga ago the youngest basalts occur around the aristarchus plateau and the kepler crater which are located in the central region of the pkt it is likely that heating in the crust due to the concentration of heat producing elements in the pkt delayed cooling of a partial melting zone in the underlying mantle in contrast with previous basalt dating in this region our results indicate a higher correlation between ages and spectral types of mare basalts the young mare units in the pkt tend to have spectral types corresponding to high titanium contents while low titanium basalts occur mainly in the early stage the titanium variation in mare basalts may reflect vertical heterogeneity in tio2 content in the upper mantle beneath the pkt

the eruptive history of the patzcuaro lake area in the michoacan guanajuato volcanic field central mexico field mapping c 14 and 40ar 39ar geochronology abstract monogenetic volcanic fields occur in many tectonic settings representing an unpredictable and uncertain volcanic hazard the patzcuaro lake is located in the central part of the michoacan guanajuato volcanic field mgvf field mapping of an area of 560 km2 stratigraphy and new radiometric ages 40ar 39ar and 14c aided in the identification of 45 individual volcanic landforms formed during the past 3 9 ma these landforms comprise five medium size shield volcanoes 25 scoria cones 10 lava domes two lavas associated to scoria cones one fissural lava flow and two volcanic complexes these volcanic edifices erupted a minimum volume of 20 km3 since pliocene with an output rate of 0 02 km3 ka chemical composition of magmas ranges from 47 6 to 65 3 wt silica being dominantly andesites 76 vol followed by basaltic andesites 12 vol dacites 9 vol and basalts 3 vol volcanic products vary from mainly andesitic during the pliocene basaltic to dacitic during the pleistocene and basaltic andesitic to andesitic during the holocene all these rocks are the result of low dipping slab subduction related magmatism alignment of cones and structures follow ne sw n s and e w directions the youngest faults are associated with the e w morelia acambay fault system with historic earthquake activity the volcanic complexes el estribo and la muela have cone collapses to the north that correspond with the direction of maximum regional extension associated with the e w fault system the 3 9 ma history of monogenetic volcanism around the patzcuaro lake demonstrates that monogenic fields can be long lived volcanic features