lower crustal deformation beneath the central transverse ranges southern california results from the los angeles region seismic experiment 1 we present a p wave velocity model derived from active source seismic data collected during the 1994 los angeles region seismic experiment our model extends previously published upper crustal velocity models to mantle depths our model was developed by both ray tracing through a layered model and calculating travel times through a gridded model it includes an 8 km thick crustal root centered beneath the surface trace of the san andreas fault north of the highest topography in the san gabriel mountains a simple mass balance calculation suggests that 36 km of north south shortening across the san andreas fault in the central transverse ranges could have formed this root if north south compression began when the big bend in the san andreas fault formed at 5 ma 36 km of shortening implies a north south contraction rate of 7 1 mm yr across the central transverse ranges if instead north south compression began when the transverse ranges formed at 3 4 3 9 ma 36 km of shortening implies a contraction rate of 9 2 10 6 mm yr north of the san andreas fault the mojave desert crust has a low velocity 6 3 km s mid and lower crust and a 28 km deep moho south of the san andreas fault beneath the los angeles and san gabriel valley basins there is a fast 6 6 6 8 km s thick 10 12 km lower crust with a 27 km deep moho farther south still the lower crust of the continental borderland is fast 6 6 6 8 km s and thin 5 km with a shallow 22 km deep moho

impact of landslides on soil characteristics implications for estimating their age the slopes of mount elgon a complex volcano at the border between uganda and kenya are frequently affected by landslides with disastrous effects on the livelihood of its population since local people greatly depend on the land for crop production this paper examines if and how fast physico chemical characteristics in landslide scars recover a chronosequence of 18 landslides covering a period of 103 years was sampled in order to explore differences between topsoil inside and outside landslide scars for each landslide two topsoil samples were taken within the landslide and two in nearby undisturbed soils to compare their physico chemical characteristics samples inside the landslides were located at the transition zone between the depletion and accumulation zone which is situated at the contact line between the plan concave and plan convex section of the landslide no differences were found for available phosphorus ca2 mg2 content or for the fine earth texture recent landslides had however lower content of soil organic carbon oc and k and higher content of rock fragments and na than the adjacent soils soil oc content increased significantly with age and reached levels of the corresponding undisturbed soils after ca 60 years older landslides had even higher oc contents than soils adjacent to the landslide hence landslide scars act as local carbon sink we suggest that the occurrence of rock fragments in the topsoil is a useful indicator for mapping past landslides moreover the difference in soil oc content between landslide scars and adjacent soil could be used for estimating the age of landslides in data poor regions

crustal extension and magmatic processes cocorp profiles from death valley and the rio grande rift new crustal scale information on the interaction between normal faulting and magmatic activity is provided by recent cocorp deep seismic reflection profiles in death valley california and by reprocessing of the cocorp data from the socorro area of the rio grande rift new mexico the most striking feature on the seismic sections from these areas is a prominent subhorizontal series of reflectors at mid crustal depth previous studies have suggested that thin tabular magma bodies lie within the mid crustal reflective zones in addition because they are traced without apparent offset beneath faults both mapped at the surface and interpreted from the cocorp data these mid crustal horizons are here inferred to be detachments or zones of tectonic decoupling upper crustal cenozoic faults do not appear to penetrate deeper than 15 km in death valley and 13 km in the rio grande rift in death valley these faults are relatively planar with moderate dips 20 to 35 and appear to bound large basement rocks one such zone of normal faults can be traced from the magma body inferred at 15 km depth beneath central death valley to the surface location of a 690 000 yr old basaltic cinder cone listric and low to moderate angle normal faults are evident on the reprocessed new mexico data and constitute the structural component of upper crustal extension in particular a listric master fault traceable to depths as great as 13 km is inferred to underlie the albuquerque basin unlike the death valley data no faults are observed to merge with the socorro magma body per se rather subhorizontal to moderately west dipping packages of reflections are imaged between the base of the faulted upper crust 13 km depth and the mid crustal magma body about 20 km depth the middle crust marks a major rheological boundary between the faulted upper crust and a ductile lower crust extending by penetrative flow and intrusion events seen in the middle and lower crust are generally subhorizontal and prominent layering is observed a band of reflections attributed to the crust mantle boundary is evident on most seismic sections the upper mantle appears seismically transparent on some of the profiles the events attributed to the base of the crust are the deepest in a series of strong and continuous reflections at least one of which is a layer of magma this association supports the suggestion that magmatic intrusions are a probable cause for the high reflectivity observed in the deep crust of many extensional terranes

crustal structure and seismicity distribution adjacent to the pacific and north america plate boundary in southern california new three dimensional 3 d v p and v p v s models are determined for southern california using p and s p travel times from local earthquakes and controlled sources these models confirm existing tectonic interpretations and provide new insights into the configuration of geological structures at the pacific north america plate boundary the models extend from the u s mexico border in the south to the southernmost coast ranges and sierra nevada in the north and have a 15 km horizontal grid spacing and an average vertical grid spacing of 4 km down to 22 km depth the heterogeneity of the crustal structure as imaged by v p and v p v s models is larger within the pacific plate than the north american plate similarly the relocated seismicity deepens and shows more complex 3 d distribution in areas of the pacific plate exhibiting compressional tectonics the models reflect mapped changes in the lithology across major geological terranes such as the mojave desert the peninsular ranges and the transverse ranges the interface between the shallow mono of the continental borderland and the deep moho of onshore california forms a broad zone to the north beneath the western transverse ranges ventura basin and the los angeles basin and a narrow zone to the south along the peninsular ranges the near surface increase in velocity from the surface to up to 8 km depth is rapid and has a logarithmic shape for stable blocks and mountain ranges but is slow with a linear shape for sedimentary basins at midcrustal depths a rapid increase in v p is imaged beneath the sediments of the large sedimentary basins while beneath the adjacent mountain ranges the increase is small or absent

seismic structure of the lithosphere from teleseismic converted arrivals observed at small arrays in the southern sierra nevada and vicinity california 21 well distributed teleseisms 30 to 100 distance were recorded by mixed broad band bb and short period sp seismic arrays at mineral king mk and horseshoe meadow hm in the southern sierra nevada and at darwin plateau dp between the inyo and argus ranges these arrays permit identification and separation of direct p and s arrivals reflections from topography scattered energy and arrivals from different back azimuths multipath arrivals p to s conversions can be identified from beamed bb or sp seismograms least squares time domain processing recovered single event receiver functions from these beamed seismograms converted phases attributable to the moho are clear and uncomplicated at dp ps p times of 3 9 4 2 s correspond to crustal thicknesses of 31 33 km assuming a mean p crustal velocity of 6 2 km s and a poisson s ratio of 0 255 ps p times at hm eastern sierra are 3 9 4 6 s 32 37 km excepting some unusual seismograms from events at back azimuths of 225 239 mk western sierra times for ps p show a strong e w asymmetry 3 9 4 1 s 31 33 km from the east and 4 8 5 3 s 39 42 km from the west the mk arrivals from the east are multiple and substantially weaker by comparison with hm and dp these results confirm the absence of a thick crust under the southern high sierra inferred from both a refraction experiment coincident with this experiment and some earlier studies at dp the moho event follows an intracrustal negative polarity event defining the top of an s wave low velocity zone this feature dips west under the sierran crest at hm but is absent farther west at mk this feature appears to be a manifestation of extensional strain and thus indicates that the surficially undeformed sierra overlies a tectonized lower crust sub moho energy is absent under the basin and range dp but is conspicuous under the high sierra at positive arrivals 7 3 s mk and 9 s hm after the p these arrivals might be from the base of a low velocity low density upper mantle body supporting the sierra

the deep crustal structure of the mojave desert california from cocorp seismic reflection data cocorp seismic reflection profiling in the western and northern mojave desert of southern california has revealed the presence of numerous major low angle reflecting horizons within the crust these complex though laterally continuous horizons are interpreted to represent major southwesterly dipping crustal fault zones and as such they place important constraints on the tectonic evolution of the region the upper most horizon is interpreted to be the rand thrust which where exposed places precambrian and late cretaceous crystalline rocks over possibly younger pelona rand orocopia schist this reflecting horizon extends for 25 km southwest of the rand mountains where it appears to be truncated at a depth of about 7 4 km by another horizon which may be a later low angle normal fault the other reflecting horizons are not traceable to the surface and so greater ambiguity remains in their interpretation the most prominent of these horizons occurs at midcrustal depths 15 6 km exhibits a ramp and flat geometry and extends over the northern area of the mojave survey into the basin and range province a lower horizon at depths of 20 30 km in the northern part of the survey area is antiformal and appears to terminate above a flat and relatively continuous moho depth horizon the crustmantle transition appears to be represented by a continuous series of reflections which occur at about 10 s 33 km in the north of the survey and at about 8 9 s 26 29 km in the south these reflections are offset in the vicinity of the town of mojave the deep intracrustal fault zones inferred from the cocorp survey may represent 1 the deep crustal continuation of the system of mesozoic thrusts which crops out in southern nevada and southeastern california 2 late cretaceous to early cenozoic northeast vergent thrusts related to the uplift of the pelona orocopia rand schist or 3 low angle normal faults related to early miocene northeast southwest directed crustal extension the cocorp survey also traversed the major strike slip faults that bound the mojave block the san andreas fault zone appears to truncate reflectors at depths of 6 8 and 20 km within the mojave basement suggesting that it is a major vertical feature which extends to at least 20 km depth conversely the garlock fault does not offset an underlying reflecting horizon which occurs at 9 km depth and therefore appears to be a relatively shallow crustal feature

regional mapping of the crustal structure in southern california from receiver functions lateral variations of the crustal structure in southern california are determined from receiver function rf studies using data from the southern california seismic network broadband stations and los angeles regional seismic experiment surveys the results include crustal thickness estimates at the stations themselves and where possible cross sections are drawn the large scale moho depth variation pattern generally correlates well with the current status of the mesozoic batholith deep moho of 35 39 km is observed beneath the western peninsula ranges sierra nevada and san bernardino mountains where the batholith is relatively intact and shallow moho of 26 32 km is observed in the mojave desert where the batholith is highly deformed and disrupted high resolution lateral variations of the crustal structure for individual geographic provinces are investigated and distinctive features are identified the crustal structure is strongly heterogeneous beneath the central transverse ranges and deep moho of 36 39 km is locally observed beneath several station groups in the western san gabriel mountains moho is relatively flat and smooth beneath the western mojave desert but gets shallower and complicated to the east anomalous rfs are observed at two stations in the eastern mojave desert where a moho step of 8 10 km is found between the nw and se back azimuthal groups of station dan in the fenner valley asymmetric extension of the salton trough is inferred from the moho geometry depth extension of several major faults such as the san andreas fault and san gabriel fault to the moho is inferred

estimating crustal thickness in southern california by stacking pmp arrivals we use observations of the moho reflected phase pmp to constrain crustal thicknesses and upper mantle velocities in southern california we stack normalized absolute values of seismograms from local events in time and range bins after aligning on the initial p arrival and applying a range correction to adjust the various source depths to the surface although most individual seismograms do not allow accurate determination of a pmp arrival time imaging the whole data set in this way shows clear pmp arrivals at ranges from about 90 km to over 250 km pmp pg and pmp pn differential times can be measured from the image and used to estimate the moho depth and upper mantle velocity for southern california we obtain an average crustal thickness of 28 km and an upper mantle velocity of 7 8 km s next we map lateral variations by repeating this procedure for stacks of subsets of the data in which the traces are grouped in caps by moho reflection point estimates of moho depth range from 18 km in the salton trough to 33 km beneath the eastern transverse ranges and 36 km beneath the southernmost sierra nevada the upper mantle velocities generally increase from southwest to northeast across the region we also map postcritical pmp pg amplitudes which vary by a factor of 4 with the highest amplitudes in the northwest mojave desert preliminary experiments with stacking sms arrivals indicate strongly correlated sms and pmp amplitude variations these results provide a guide to source receiver paths that may produce anomalously strong moho reflected phases during future earthquakes

rates of pedogenic processes in volcanic landscapes of late pleistocene to holocene age in central mexico abstract the transmexican volcanic belt and its many volcanic fields of different ages offer good opportunities to study soil development on volcanic tephra of intermediate to basaltic composition we studied a soil chronosequence within the sierra chichinautzin volcanic field scvf south of the basin of mexico and aimed to establish the rates of pedogenic processes this field has been active for around 50 000 years and produced 221 cinder cones with their respective lava flows we selected 11 sites located on 14 c dated lava flows of ages between 1800 and 30 500 bp at 3100 3200 m above sea level covered with pine fir forest with an ustic soil moisture regime and an isomesic soil temperature regime we also included a younger site 1000 bp and three older sites 100 000 years two at 3100 masl and one at 2600 masl from nearby volcanic fields to widen the time frame of the chronosequence soil profile samples were analysed for total organic carbon as well as for mineral neoformations related to clay contents selective chemical extractions and x ray diffraction analyses within the scvf the total soil thickness carbon accumulation and al si and fe extracted with acid ammonium oxalate increased linearly with age on surfaces up to 10 000 years old at rates of 19 cm ky 1 4 1 kg c m 2 ky 1 4 6 kg al 2 7 kg si and 2 kg fe m 2 ky 1 respectively crystalline clay and iron oxide formation reach a maximum at the oldest site located at 2600 masl of 1650 kg clay m 2 and 70 kg fe d m 2 their increase is linear up to ages of 10 000 years at rates of 22 kg clay m 2 ky 1 and 2 8 kg fe d m 2 ky 1 thereafter the rates are much slower allophane and allophane like minerals dominate in the clay fraction at all sites of the chronosequence and small amounts of halloysite can be identified in soils older than 6200 years while kaolinite was only identified at the three oldest sites 100 000 years the linear increases of all indicators of pedogenesis in the first 10 000 years are presumably driven by recurrent tephra deposition during this time frame thereafter erosion and colluviation processes seem to disturb pedogenesis changing its rates and redistributing its products in the landscape

base saturation nutrient cation and organic matter increases during early pedogenesis on landslide scars in the luquillo experimental forest puerto rico we evaluate data from a chronosequence study of landslide scars ranging in age from 1 55 yr in the luquillo experimental forest lef a subtropical lower montane wet forest sensu holdridge in eastern puerto rico surface mineral soil 0 10 cm base saturation index bsi values increase during primary succession in the lef r 0 85 p 0 001 both bsi values and major nutrient cation concentrations are extremely low on new landslide scars during the course of the 55 yr chronosequence major nutrient cation concentrations are positively correlated with soil organic matter som content p 0 079 and not with clay content p 0 794 when data collected from plots representing the two dominant late succession vegetation associations are added to the analysis nutrient cation concentrations correlate significantly with both som p 0 001 and clay content p 0 033 our data show that when initial conditions are oligotrophic both nutrient cation pools and bsi values can increase in the surface mineral soil during early pedogenesis we discuss exogenic litter input substrate weathering and precipitation as potential sources for nutrient cations in these soils we further suggest that production and decomposition of som is the dominant process controlling capture retention and intra ecosystem cycling of nutrient cations in these forests

slopewash surface runoff and fine litter transport in forest and landslide scars in humid tropical steeplands luquillo experimental forest puerto rico rainfall slopewash the erosion of soil particles surface runoff and fine litter transport at humid tropical steepland sites in the luquillo experimental forest puerto rico 188 20 n 658 45 w were measured from 1991 to 1995 hillslopes underlain by 1 cretaceous tuffaceous sandstone and siltstone in subtropical rain tabonuco forest with vegetation recovering from hurricane hugo 1989 and 2 tertiary quartz diorite in subtropical lower montane wet colorado and dwarf forest with undisturbed forest canopy were compared to recent landslide scars monthly surface runoff on these very steep hillslopes 248 to 438 was only 0 2 to 0 5 per cent of monthly rainfall slopewash was higher in sandy loam soils whose parent material is quartz diorite averaging 46 g m 2 a 1 than in silty clay loam soils derived from tuffaceous sandstone and siltstone where the average was 9gm 2 a 1 annual slopewash of 100 to 349 gm 2 on the surfaces of two recent small landslide scars was measured initially but slopewash decreased to only 3 to 4 g m 2 a 1 by the end of the study the mean annual mass of fine litter mainly leaves and twigs transported downslope at the forested sites ranged from 5 to 8 g m 2 and was lower at the tabonuco forest site where post hurricane hugo recovery is still in progress mean annual fine litter transport was 2 5gm 2 on the two landslide scars copyright 1999 john wiley sons ltd

seismic reflection constraints on the structure of the crust beneath the san bernardino mountains transverse ranges southern california a 30 km long n s seismic reflection line was shot by california consortium for crust studies calcrust across the southern mojave desert and onto the northern flank of the san bernardino mountains in southern california on the northern end of the seismic section the reflectivity increases markedly in the midcrust at a depth corresponding to a two way travel time of 4 to 5 s 12 15 km suggesting a transition between nonreflecting brittle upper crust and reflecting ductile lower crust the high reflectivity disappears at about 8 s 24 km and may be correlated with a change in seismic velocity in the lower crust from 6 3 km s to 6 8 km s a band of reflectivity between 9 5 and 10 s 27 30 km is believed to represent the moho the midcrustal relectivity transition and moho both deflect downward toward the san bernardino mountains uplift over the entire length of the profile the deflection of the midcrustal transition 12 appears greater than that of the moho 6 resulting in a thinning of the lower crust to the south beneath the uplift in addition the midcrustal transition coincides with the base of the seismogenic zone brittle ductile transition which is also dipping southward beneath the san bernardino mountains while the moho deflection is consistent with elastic flexure resulting from edge loading by the san bernardino mountains which have been thrust over the mojave block it is suggested that the thinning of the lower crust beneath the san bernardino mountains is a result of north directed ductile flow in response to loading by the over thickened upper crust since a portion of the load is transmitted through the lower crust to the moho the time constant for flow equilibrium must be of the order of or greater than that for the time of uplift 2 m y

observations and sampling of an ongoing subsurface eruption of kavachi volcano solomon islands may 2000 a serendipitous encounter with an erupting shallow submarine volcano in the solomon islands provided a rare opportunity to map and sample the dispersal of volcanogenic emissions into the surrounding water column kavachi episodically active since at least 1939 is a forearc volcano located on the pacific plate only 30 km northeast of its convergent boundary with the downgoing indo australian plate during 14 may 2000 we observed explosive phreatomagmatic eruptions at several minute intervals creating a complex distribution of plumes of volcanic glass shards throughout the water column at a distance of 1 5 km from the summit at distances of 4 5 km shallow water 3 he fe and mn one sample only but not in co 2 we infer that the volcano flanks were essentially impermeable to fluid emissions and that the observed particle halo was created by magma shattering and resuspension most magmatic and hydrothermal fluids were thus discharged directly from the summit into the atmosphere

linking geomorphology weathering and cation availability in the luquillo mountains of puerto rico abstract we explored the links between geomorphology weathering and cation availability across the most common forest types and geologic provinces in the el yunque national forest puerto rico our goal was to connect the controls on primary mineral supply to soil with stocks of plant available cations we established a network of 216 soil profiles comprising toposequences ridges slopes and valleys in three forest types colorado palm and tabonuco on two parent rock types quartz diorite and volcaniclastic in a factorial design the landscape underlain by quartz diorite is divided into lower slopes that are eroding rapidly in response to renewed uplift in the last 5 ma and those above a regional knickpoint where remnant landforms are eroding more slowly quartz diorite derived soils 0 80 cm below the knickpoint have lost significantly less calcium ca magnesium mg and potassium k relative to parent material 80 65 and 57 respectively than those above it which have lost 95 81 and 83 p 90 of all base cations relative to parent material while geology and geomorphology exert the most control on the degree of soil weathering as measured by total soil cation loss relative to parent material exchangeable cations are influenced by geologic biologic and meteoric factors tabonuco forests have significantly higher exchangeable cation stocks 0 80 cm than colorado forests even in the 500 700 m elevation zone where the two forest types are not correlated with elevation p 0 02 0 005 and 0 002 for ca mg and k respectively forest type explains 30 of the variance in exchangeable mg and k stocks but only 10 of the variance in exchangeable ca quartz diorite derived soils below the knickpoint have 2 more exchangeable ca than those above it and within that rapidly eroding region sites closest in elevation to the knickpoint have 2 more again the isotopic composition of bulk soil and exchangeable strontium suggests that the high ca stocks below and near the knickpoint are mostly derived from primary mineral weathering whereas above the knickpoint exchangeable ca is supplied by atmospheric deposition these data demonstrate that regional uplift lithology weathering atmospheric inputs and forest communities combine to shape cation availability across the luquillo landscape and we hypothesize that similar interactions are important in other montane tropical forests

lithospheric instability beneath the transverse ranges of california recent high resolution seismic experiments reveal that the crust beneath the san gabriel mountains portion of the transverse ranges thickens by 10 15 km contrary to earlier studies associated with the transverse ranges there is an anomalous ridge of seismically fast upper mantle material extending at least 200 km into the mantle this high velocity anomaly has previously been interpreted as a lithospheric downwelling both lithospheric downwelling and crustal thickening are associated with the oblique convergence of pacific and north america plates across the san andreas fault though it seems likely that the lithospheric downwelling is driven at least partly by gravitational instability of the cold lithospheric mantle we show by means of numerical experiment that the balance between buoyancy forces that drive deformation and viscous stresses that resist deformation determines the geometry of crustal thickening and mantle downwelling we use a simple two layered lithospheric model in which dense lithospheric mantle overlies relatively inviscid and less dense asthenosphere and is overlain by buoyant crust external plate motion drives convergence which is constrained by boundary conditions to occur within a central convergent zone of specified width a fundamental transition in the geometry of downwelling is revealed by our experiments for slow convergence or low crustal viscosity downwelling occurs as multiple sheets on the margins of the convergent zone for fast convergence or crust that is stronger than mantle lithosphere a single downwelling occurs beneath the center of the convergent zone this complexity in the evolution of the system is attributed to the interaction of crustal buoyancy with the evolving gravitational instability in order for a narrow downwelling slab to have formed beneath the transverse ranges within the last 5 myr the effective lithospheric viscosity of the convergent region is at most about 10 20 pa s

crustal thickness of the peninsular ranges and gulf extensional province in the californias we estimate crustal thickness along an east west transect of the baja california peninsula and gulf of california mexico and investigate its relationship to surface elevation and crustal extension we derive moho depth estimates from p to s converted phases identified on teleseismic recordings at 11 temporary broadband seismic stations deployed at 318n latitude depth to the moho is 33 63 km near the pacific coast of baja california and increases gradually toward the east reaching a maximum depth of 40 64 km beneath the western part of the peninsular ranges batholith the crust then thins rapidly under the topographically high eastern peninsular ranges and across the main gulf escarpment crustal thickness is 15 18 62 km within and on the margins of the gulf of california the moho shallowing beneath the eastern peninsular ranges represents an average apparent westward dip of 258 this range of moho depths within the peninsula ranges as well as the sharp east west gradient in depth in the eastern part of the range is in agreement with earlier observations from north of the international border the moho depth variations do not correlate with topography of the eastern batholith these findings suggest that a steeply dipping moho is a regional feature beneath the eastern peninsular ranges and that a local airy crustal root does not support the highest elevations we suggest that moho shallowing under the eastern peninsular ranges reflects extensional deformation of the lower crust in response to adjacent rifting of the gulf extensional province that commenced in the late cenozoic support of the eastern peninsular ranges topography may be achieved through a combination of flexural support and lateral density variations in the crust and or upper mantle

crustal thickness variations beneath the peninsular ranges southern california we investigate the crustal thickness under the peninsular ranges using p to s converted phases of teleseismic body waves recorded on a temporary broadband seismometer array and isolated by the receiver function method ps minus p times at sites west of a compositional boundary that separates the peninsular ranges batholith into east and west zones indicate a relatively flat deep moho ps minus p times at sites east of the compositional boundary decrease eastward moho depth estimates made from the ps delays and crustal velocities from seismic tomography indicate a relatively constant 36 to 41 km thick crust in the western zone in the eastern zone the crust thins rapidly from 35 km thick at the compositional boundary to 25 km at the edge of the salton trough a lateral distance of 30 km the lack of correlation between topography and moho depths suggests compensation via lateral density variations in the lower crust or upper mantle we propose that the compositional boundary decouples the eastern and western portions of the batholith and that the eastern portion has thinned in response to regional miocene extension or salton trough rifting or both

lithospheric deformation beneath the san gabriel mountains in the southern california transverse ranges high resolution tomographic images from los angeles region seismic experiment larse array and southern california seismic network scsn teleseismic data suggest that the entire lithosphere below the san gabriel mountains and san andreas fault in the transverse ranges has thickened in a narrow vertical sheet p wave travel time inversions of the combined data support the presence of the well documented upper mantle high velocity anomaly that extends 200 km into the mantle under the northernmost los angeles basin and transverse ranges and is associated with mantle downwelling due to oblique convergence we find that the high velocity high density upper mantle anomaly comprises a 60 80 km wide sheet of mantle material that lies directly below a substantial crustal root in the san gabriel mountains the velocity perturbations are as large as 3 in the anomaly corresponding to a 2 density increase the tomographic images suggest that deformation in the ductile lower crust and mantle lithosphere may be partially coupled mechanically and thermally if the thickening is occurring together in response to convergence and that it may be a local compressional feature

tomographic image of the southern california mantle p wave teleseismic travel time delays recorded by the southern california array are inverted by the method of backprojection tomography to obtain images of variations in the p wave velocity structure to a depth of 750 km two major upper mantle features arc resolved one beneath the transverse ranges region and another beneath the salton trough region the transverse ranges feature appears as a curtainlike east trending high velocity anomaly this feature is 60 km thick extends most deeply on its eastern end to 250 km and attains a maximum velocity 3 greater than average southern california mantle of the same depth the salton trough feature which is not as well resolved as the transverse ranges feature is composed of low velocities in the upper 70 100 km these p wave velocities arc depressed 3 4 compared to average southern california mantle tests of the inversion indicate the major aspects of the imaged structure are authentic

landslide induced changes of soil physicochemical properties in xitou central taiwan abstract steep mountain terrain fractured geological environments and intense precipitation events are primary factors that contribute to frequent landslides in mountainous regions landslides exert an immense impact on forest ecosystems and substantially change soil properties understanding these changes is crucial to facilitating subsequent forest revegetation and management in this study the effects of landslide on soil physicochemical properties were investigated in a moist montane forest ecosystem in xitou central taiwan we established a dataset comprised historical soil survey data obtained in 1976 and data from soil samples taken in 2012 at the same locations to compare differences in soil properties after landslide deposition and also conducted soil sampling along a landslide nonlandslide affected sequence to determine how the degree of landslide deposition affected soil physicochemical properties the results indicated that rock fragment content soil ph value bulk density inorganic carbon and base saturation increased following landslide deposition and that severe landslide deposition caused more substantial increases by contrast the thicknesses of the o and a horizons soil organic carbon total nitrogen and cation exchange capacity significantly decreased following landslides these decreases were more substantial with increasing degree of landslide deposition exchangeable potassium calcium magnesium and available phosphorus content however were unaffected by landslide deposition the results demonstrated that soil physicochemical properties were significantly altered after landslide deposition these resultant changes particularly in regard to high soil ph value poor structure and low soil organic carbon and total nitrogen are expected to influence functions in forest ecosystems

three dimensional vp and vp vs velocity models of the los angeles basin and central transverse ranges california we use p and s arrival times from 5225 earthquakes and 53 explosions recorded by the southern california seismographic network to invert for the three dimensional p velocity v p and the p and s velocity ratio v p v s in the central transverse ranges and the los angeles basin to model long wavelength features of the velocity structure we invert for the models by interpolating models determined successively from a sparse medium to a dense grid with 40 20 and 10 km spacing of horizontal grid nodes layers of grid nodes are placed at depths of 1 4 6 8 12 16 and 20 km the data variance decreased about 80 in the gradational inversion ample data from the 1994 northridge and other earthquake sequences the rich background seismicity and the dense station distribution along with controlled sources made the model well resolved except along the edges to the southwest in the offshore region and at depths greater than 20 km the v p model images the shape of the los angeles and east ventura basins down to depths of 8 and 12 km three low velocity areas at 1 km depth in the los angeles basin that coincide with recent sediment depositional areas are also imaged the north edge of the peninsular ranges the santa monica and the san gabriel mountains form discontinuous high velocity ridges extending to depths of 20 km the high v p v s ratios in the near surface are consistent with high pore fluid pressures in the basin sediments at depth beneath the east ventura basin the high v p v s and high v p suggest the presence of ophiolitic assemblages or mid miocene volcanics in contrast a body with normal v p and low v p v s that is identified in the upper crust beneath santa monica bay may be a fragment of quartz rich continental crust the v p model of both the ventura and the los angeles basins shows features that suggest deformation of the hanging wall or basin closure at seismogenic depths of 16 km the hypocenters of moderate sized and large earthquakes are located within or adjacent to high v p velocity bodies in most cases these high velocity bodies form the upper block consistent with shortening of the lower crust as described in thick skinned tectonic interpretations

the role of soil processes in determining mechanisms of slope failure and hillslope development in a humid tropical forest eastern puerto rico abstract translational failures with associated downslope earthflow components and shallow slides appear to be the primary mechanism of hillslope denudation in the humid tropical forests of the mountains of eastern puerto rico in situ weathering of quartz diorite and marine deposited volcaniclastics produces residual soil saprolite up to 21 m deep weathered rock profiles discontinuous zones of contrasting density and permeability particularly in quartz diorite slopes at 0 5 m and between 3 and 7 m create both pathways and impedances for water that can result in excess pore pressures and ultimately aid in determining the location of failure planes and magnitudes of slope failures in combination with relict fractures which create planes of weakness within the saprolite and the potential significance of tensile stresses in the upper zone of saprolite hypothesized to be caused by subsurface soil creep shear failure can then occur during or after periods of heavy rainfall results of in situ shear strength testing show negative y intercepts on the derived mohr coulomb failure envelopes approximately 50 of all tests that are interpreted as apparent tensile stresses observation of tension cracks 1 2 m deep support the test data subsurface soil creep can cause extension of the soil and the development of tensile stresses along upper slope segments shear strength data support this hypothesis for both geologic types apparent values of maximum and mean tensile stress are greatest along upper slopes 16 5 and 6 29 kpa previously documented maximum rates of downslope movement coincided with local minima of shear strength and the shear strength minimum for all tests was located near 0 5 m below land surface the shallow zone of contrasting permeabilities these results indicate that subsurface soil creep a slow semi continuous process may exert a profound influence on rapid shallow slope failures in saprolitic soils data indicate that cove slopes in quartz diorite tend to be the most unstable when saturation levels reach 75 deep failures 7 m deep appear the most critical but not the most frequent because pore pressure build up will occur more rapidly in the upper perched zone of translocated clays before reaching the lower zone between 3 and 7 m frequent shallow failures could reduce the probability of deeper failures by removing overburden and reducing shear stress at depth deep failures are more likely to result from storm events of great duration and intensity sixty six naturally occurring and more than 100 road related landslides were mapped forest elevations exceed 1000 m but the majority of these failures were found between 600 and 800 m in elevation this appears to be the area where there is sufficient concentration of subsurface water to result in excess pore pressures the high percentage of slope failures in the 600 800 m range relative to the percentage at higher elevations suggests that differences in soil water processes are responsible for the form of these mountain slopes steep linear segments are maintained at higher elevations slope angles are reduced in the 600 800 m range by frequent shallow slides creating a largely concave surface in combination slope segments above 800 m and those between 600 and 800 m produce the characteristic form of the mountains of eastern puerto rico

phosphorus and iron cycling in deep saprolite luquillo mountains puerto rico abstract rapid weathering and erosion rates in mountainous tropical watersheds lead to highly variable soil and saprolite thicknesses which in turn impact nutrient fluxes and biological populations in the luquillo mountains of puerto rico a 5 m thick saprolite contains high microorganism densities at the surface and at depth overlying bedrock we test the hypotheses that the organisms at depth are limited by the availability of two nutrients p and fe many tropical soils are p limited rather than n limited and dissolution of apatite is the dominant source of p we document patterns of apatite weathering and of bioavailable fe derived from the weathering of primary minerals hornblende and biotite in cores augered to 7 5 m on a ridgetop as compared to spheroidally weathering bedrock sampled in a nearby roadcut iron isotopic compositions of 0 5 n hcl extracts of soil and saprolite range from about 56 fe 0 to 0 1 throughout the saprolite except at the surface and at 5 m depth where 56 fe 0 26 to 0 64 the enrichment of light isotopes in hcl extractable fe in the soil and at the saprolite bedrock interface is consistent with active fe cycling and consistent with the locations of high cell densities and fe ii oxidizing bacteria identified previously to evaluate the potential p limitation of fe cycling bacteria in the profile solid state concentrations of p were measured as a function of depth in the soil saprolite and weathering bedrock weathering apatite crystals were examined in thin sections and an apatite dissolution rate of 6 8 10 14 mol m 2 s 1 was calculated while surface communities depend on recycled nutrients and atmospheric inputs deep communities survive primarily on nutrients released by the weathering bedrock and thus are tightly coupled to processes related to saprolite formation including mineral weathering while low available p may limit microbial activity within the middle saprolite fluxes of p from apatite weathering should be sufficient to support robust growth of microorganisms in the deep saprolite

soil properties on a chronosequence of landslides in montane rain forest ecuador to assess the impact of landslides on soil fertility in south ecuador we compared the properties of shallow translational debris slides with those of adjacent undisturbed soils a chronosequence of four small landslides ca 0 5 ca 2 3 ca 8 10 and ca 20 years old was selected on a 30 50 forest covered east facing slope of the eastern cordillera at 1900 2300 m above sea level a s l all soils were dystric cambisols the mean mass of the soil organic layer sum of all o horizons increased in the order landslide head 46 t ha 1 central part track 101 t ha 1 foot 102 t ha 1 reference soils 291 t ha 1 implying a variation in nutrient storage of the same order in the head area only the oldest landslide had an organic layer all mineral soils were acidic ph in h2o of the a horizon 3 4 5 2 the effective cec of the a horizon ranged from 22 to 141 mmolc kg 1 and the base saturation from 13 to 54 none of these properties was consistently different between landslide and reference soils the a horizons of the soil in the landslide foot area had greater concentrations of most nutrients than those in the landslide head area however differences were not significant the nutrient concentrations in the landslide foot area resembled those in the a horizons of the reference soils thus the most obvious change in soil properties caused by the landsliding was partial or complete removal of the organic layer which was not restored during the ca 20 years covered by the chronosequence this decreased the topsoil fertility of the landslide area

impact of hydrologically driven hillslope erosion and landslide occurrence on soil organic carbon dynamics in tropical watersheds the dynamics of soil organic carbon soc in tropical forests play an important role in the global carbon c cycle past attempts to quantify the net c exchange with the atmosphere in regional and global budgets do not systematically account for dynamic feedbacks among linked hydrological geomorphological and biogeochemical processes which control the fate of soc here we quantify effects of geomorphic perturbations on soc oxidation and accumulation in two adjacent wet tropical forest watersheds underlain by contrasting lithology volcaniclastic rock and quartz diorite in the luquillo critical zone observatory this study uses the spatially explicit and physically based model of soc dynamics tribs eco triangulated irregular network based real time integrated basin simulator erosion and carbon oxidation and measurements of soc profiles and oxidation rates our results suggest that hillslope erosion at the two watersheds may drive c sequestration or co2 release to the atmosphere depending on the forest type and land use the net erosion induced c exchange with the atmosphere was controlled by the spatial distribution of forest types the two watersheds were characterized by significant erosion and dynamic replacement of upland soc stocks results suggest that the landscape underlain by volcaniclastic rock has reached a state close to geomorphic equilibrium and the landscape underlain by quartz diorite is characterized by greater rates of denudation these findings highlight the importance of the spatially explicit and physical representation of c erosion driven by local variation in lithological and geomorphological characteristics and in forest cover this article is protected by copyright all rights reserved

some highly weathered soils of puerto rico 1 morphology formation and classification abstract this is part 1 of a study concerning the pedology of eleven soils of puerto rico which represent the range of highly weathered soils of this island six oxisols four ultisols and one inceptisol are discussed the environmental conditions and profiles studied are described in detail soil formation in response to pedogenetic factors is discussed in terms of accumulation of parent material and solum development particular emphasis is placed on soil landscape relationships the occurrence of oxisols on miocene pliocene and pleistocene surfaces is ascribed to particular geomorphic conditions ultrabasic rocks and pre weathered sediments respectively the ultisols are mainly developed in saprolites on backslopes of geologically young surfaces the inceptisol is found on a strongly weathered regolith in a perhumid mountain region in all soils studied profound weathering was largely accomplished prior to rather than as part of pedogenic alterations clay illuviation cutans could not always be positively identified in the field and the results of thin section studies did not conform with field observations in all instances this suggests the need for a re examination of the diagnostic value of argillans in soils with low activity clays and as a corollary a re evaluation of the definition and taxonomic role of the argillic horizon the soils were classified according to the u s soil taxonomy the legend for the fao unesco soil map of the world and the french soil classification system the rationales for placement in taxa of these systems and their correlations are discussed the correspondence of the puerto rican soils studied with those of other tropical areas is discribed in general terms

three dimensional seismic model of the sierra nevada arc california and its implications for crustal and upper mantle composition a three dimensional p wave velocity model of south central california from the coast ranges to the sierra nevada shows that the crust under most of the southern sierra nevada batholith has seismic velocities 5 9 6 3 km s below the continental average the crust is not much thicker on average about 35 km than in the adjacent great valley and basin and range province apart from a small northward thickening crustal root under the western sierra nevada that reaches a depth of 42 km crustal velocities above the continental average are observed beneath much of the great valley due to a high velocity body underlying the sedimentary basin and the foothills metamorphic belt 6 4 7 0 km s upper mantle velocities are generally low 7 8 km s but span a wide range 7 4 8 2 km s we display the velocity model in several cross sections and maps of moho depth and average crustal velocity the measured velocities in the upper and mid crust of the sierra nevada batholith are in good agreement with laboratory measurements on sierra nevada tonalites after corrections for density and temperature peridotite xenoliths from the eastern sierra nevada suggest strong upper mantle anisotropy which could explain some of the velocity heterogeneity in the sierra nevada mantle by the time cretaceous subduction related magmatism ceased the sierra nevada arc must have had a thick mafic lower crust yet a principal result of our work is that today the batholith has a crust of mainly felsic composition throughout a subcrustal layer with velocities below normal pn velocities 7 6 km s may indicate the presence of lower crustal material in eclogite facies

crustal structure and tectonics from the los angeles basin to the mojave desert southern california a seismic refraction and low fold reflection survey known as the los angeles region seismic experiment larse was conducted along a transect line 1 extending from seal beach california to the mojave desert crossing the los angeles and san gabriel valley basins and san gabriel mountains the chief result of this survey is an interpreted cross section that addresses a number of questions regarding the crustal structure and tectonics of southern california that have been debated for decades and have important implications for earthquake hazard assessment the results or constraints are as follows 1 the maximum depth of the los angeles basin along line 1 is 8 9 km 2 the deep structure of the sierra madre fault zone in the northern san gabriel valley is as follows the duarte branch of the sierra madre fault zone forms a buried 2 5 km high moderately north dipping buttress between the sedimentary and volcanic rocks of the san gabriel valley and the igneous and metamorphic rocks of the san gabriel mountains for deeper structure see following 3 there are active crustal decollements in southern california at middle crustal depths the sierra madre fault zone appears to sole into a master decollement that terminates northward at the san andreas fault and projects southward beneath the san gabriel valley to the puente hills blind thrust fault 4 the dip and depth extent of the san andreas fault along line 1 dips steeply 83 northward and extends to at least the moho 5 the subsurface lateral extent of the pelona schist in southern california is as follows along line 1 the pelona schist underlies much if not all of the san gabriel mountains south of the san andreas fault to middle crustal depths north of the san andreas fault it is apparently not present along the transect

the san gabriel mountains bright reflective zone possible evidence of young mid crustal thrust faulting in southern california abstract during the los angeles region seismic experiment larse a reflection refraction survey was conducted along a line extending northeastward from seal beach california to the mojave desert crossing the los angeles basin and san gabriel mountains shots and receivers were spaced most densely through the san gabriel mountains for the purpose of obtaining a combined reflection and refraction image of the crust in that area a stack of common midpoint cmp data reveals a bright reflective zone 1 s thick that dominates the stack and extends throughout most of the mid crust of the san gabriel mountains the top of this zone ranges in depth from 6 s 18 km depth in the southern san gabriel mountains to 7 5 s 23 km depth in the northern san gabriel mountains the zone bends downward beneath the surface traces of the san gabriel and san andreas faults it is brightest between these two faults where it is given the name san gabriel mountains bright spot sgmbs and becomes more poorly defined south of the san gabriel fault and north of the san andreas fault the polarity of the seismic signal at the top of this zone is clearly negative and our analysis suggests it represents a negative velocity step the magnitude of the velocity step is approximately 1 7 km s in at least one location an event with positive polarity can be observed 0 2 s beneath the top of this zone indicating a thickness of the order of 500 m for the low velocity zone at this location several factors combine to make the preferred interpretation of this bright reflective zone a young fault zone possibly a master decollement 1 it represents a significant velocity reduction if the rocks in this zone contain fluids such a reduction could be caused by a differential change in fluid pressure between the caprock and the rocks in the sgmbs near lithostatic fluid pressure is required in the sgmbs such differential changes are believed to occur in the neighborhood of active fault zones where fault value action has been postulated less likely alternative explanations for this velocity reduction include the presence of magma and a change in composition to serpentinite or metagraywacke 2 it occurs at or near the brittle ductile transition at least in the southern san gabriel mountains a possible zone of concentrated shear 3 a thin reflection rising from its top in the southern san gabriel mountains projects to the hypocenter of the 1987 m 5 9 whittier narrows earthquake a blind thrust fault earthquake with one focal plane subparallel to the reflection alternatively one could argue that the bends or disruptions in the reflective zone seen at the san gabriel and san andreas faults are actually offsets and that the reflective zone is therefore an older feature possibly an older fault zone

death valley bright spot a midcrustal magma body in the southern great basin california a previously unrecognized midcrustal magma body may have been detected by cocorp deep seismic reflection profiles in the death valley region of the southern great basin high amplitude relatively broad band reflections at 6 s 15 km are attributed to partially molten material within a subhorizontal intrusion this bright spot extends laterally at least 15 km beneath central death valley a moderately dipping normal fault can be traced from the inferred magma chamber upward to a 690 000 yr old basaltic cinder cone the fault zone is inferred to have been a magma conduit during the formation of the cinder cone vertical variations in crustal reflection character suggest that the death valley magma body may have been emplaced along a zone of decoupling that separates a faulted brittle upper crust from a more ductile and or intruded lower crust the death valley bright spot is similar to reflections recorded by cocorp in 1977 in the rio grande rift where both geophysical and geodetic evidence support the inference of a tabular magma chamber at 20 km depth

chemical weathering in a tropical watershed luquillo mountains puerto rico i long term versus short term weathering fluxes abstract the pristine rio icacos watershed in the luquillo mountains in eastern puerto rico has the fastest documented weathering rate of silicate rocks on the earth s surface a regolith propagation rate of 58 m ma 1 calculated from iso volumetric saprolite formation from quartz diorite is comparable to the estimated denudation rate 25 50 ma 1 but is an order of magnitude faster than the global average weathering rate 6 ma 1 weathering occurs in two distinct environments plagioclase and hornblende react at the saprock interface and biotite and quartz weather in the overlying thick saprolitic regolith these environments produce distinctly different water chemistries with k mg and si increasing linearly with depth in saprolite porewaters and with stream waters dominated by ca na and si such differences are atypical of less intense weathering in temperate watersheds porewater chemistry in the shallow regolith is controlled by closed system recycling of inorganic nutrients such as k long term elemental fluxes through the regolith e g si 1 7 10 8 moles m 2 s 1 are calculated from mass losses based on changes in porosity and chemistry between the regolith and bedrock and from the age of the regolith surface 200 ma mass losses attributed to solute fluxes are determined using a step wise infiltration model which calculates mineral inputs to the shallow and deep saprolite porewaters and to stream water pressure heads decrease with depth in the shallow regolith 2 03 m h2o m 1 indicating that both increasing capillary tension and graviometric potential control porewater infiltration interpolation of experimental hydraulic conductivities produces an infiltration rate of 1 m yr 1 at average field moisture saturation which is comparable with libr tracer tests and with base discharge from the watershed short term weathering fluxes calculated from solute chemistries and infiltration rates e g si 1 4 10 8 moles m 2 s 1 are compared to watershed flux rates e g si 2 7 10 8 moles m 2 s 1 consistency between three independently determined sets of weathering fluxes imply that possible changes in precipitation temperature and vegetation over the last several hundred thousand years have not significantly impacted weathering rates in the luquillo mountains of puerto rico this has important ramifications for tropical environments and global climate change

crustal structure across the san andreas fault southern california from teleseismic converted waves crustal structure along a 140 km long profile across the san andreas fault saf in southern california was imaged by stacking teleseismic p s converted phases recorded by a dense short period seismic array the crust mantle discontinuity moho is visible as a continuous feature at a depth around 30 km but is offset 6 to 8 km beneath the saf a small moho disruption can also be seen under the eastern california shear zone ecsz these results suggest that the saf and ecsz extend through the entire crust the moho upwarp under the san gabriel mountains indicates that the mountain ranges were lifted en masse as a result of crustal buckling under horizontal compression

mantle compensation of active metamorphic core complexes at woodlark rift in papua new guinea in many highly extended rifts on the earth tectonic removal of the upper crust exhumes mid crustal rocks producing metamorphic core complexes these structures allow the upper continental crust to accommodate tens of kilometres of extension but it is not clear how the lower crust and underlying mantle respond also despite removal of the upper crust such core complexes remain both topographically high and in isostatic equilibrium because many core complexes in the western united states are underlain by a flat moho discontinuity it has been widely assumed that their elevation is supported by flow in the lower crust or by magmatic underplating these processes should decouple upper crust extension from that in the mantle in contrast here we present seismic observations of metamorphic core complexes of the western woodlark rift that show the overall crust to be thinned beneath regions of greatest surface extension these core complexes are actively being exhumed at a rate of 5 10 km myr 1 and the thinning of the underlying crust appears to be compensated by mantle rocks of anomalously low density as indicated by low seismic velocities we conclude that at least in this case the development of metamorphic core complexes and the accommodation of high extension is not purely a crustal phenomenon but must involve mantle extension

the transfer of modern organic carbon by landslide activity in tropical montane ecosystems 1 geomorphic processes play an important role in the transfer and storage of carbon within steep mountainous terrain among these mass wasting stands out because of its impact on above and below ground carbon pools and its potential for releasing or sequestering carbon a combined remote sensing and gis modeling approach was used to quantify the amount and spatial redistribution of modern organic carbon mobilized by mass wasting activity in a tropical mountain setting the study focused on a population of hundreds of shallow translational landslides triggered by hurricane mitch 1998 on seven watersheds draining the southern flank of the sierra de las minas mountain range slm in central eastern guatemala results illustrate that mass wasting contributed to the transfer of 43 104mgc or 3 of the pre event c in above ground vegetation and soils for an equivalent carbon flux rate of 0 08 0 33 mgc ha 1 y 1 depending on whether we consider hurricane mitch to be a landslide triggering event with a 20 year or an 80 year recurrence interval while 30 of this carbon was delivered to hillslopes or first order streams with a presumed high potential for long term sequestration the remaining 70 was delivered to higher order streams with unknown carbon retention capabilities therefore the ultimate fate of the carbon released by landsliding is very uncertain but depending on the proportion sequestered by colluvial deposits the recurrence interval of landslide triggering events and the rate of ecosystem recuperation at the landslide failure sites mass wasting could be either a net source or sink of carbon in a simulated setting based on the slm study results in which all carbon transferred by landslides from all tropical mountains of the globe is released to the atmosphere it would represent an amount equivalent to 1 11 of the global carbon currently being released by the burning of fossil fuels meanwhile in a projected scenario where a significant proportion of the carbon transferred by landslides is retained within sedimentary deposits sequestration rates would equal 2 19 of the residual land sink

post laramide removal of the farallon slab western united states i propose that post laramide removal of the subhorizontally subducting farallon slab occurred by buckling downward along an approximately east northeast trending axis this process was accomplished by a tearing or necking separation of the subducted slab near the northern and southern boundaries of the united states and propagation of the separated edges toward the central axis of downwelling accompanied by aesthenosphic upwelling behind the trailing edges initial buckling probably began near 50 ma and slab removal was complete by 20 ma this model is based primarily on the space time evolution of the ignimbrite flare up a major mid tertiary igneous event of mantle origin which involved two propagating fronts of initiation of volcanism that followed the proposed motions of the separated slab edges as they converged on central nevada from the north and southeast post laramide uplift extension establishment of the cascadia subduction zone and active magmatism may be consequences of lithosphere scale modifications caused by the laramide removal of the slab and the resulting asthenospheric upwelling

present weathering rates in a humid tropical watershed nsimi south cameroon the study of biogeochemical and hydrological cycles in small experimental watersheds on silicate rocks common for the temperate zone has not yet been widely applied to the tropics especially humid areas this paper presents an updated database for a six year period for the small experimental watershed of the mengong brook in the humid tropics nsimi south cameroon this watershed is developed on precambrian granitoids north congo shield and consists of two convexo concave lateritic hills surrounding a large flat swamp covered by hydromorphic soils rich in upward organic matter mineralogical and geochemical investigations were carried out in the protolith the saprolite the hillside lateritic soils and the swamp hydromorphic soils biomass chemical analyses were done for the representative species of the swamp vegetation the groundwater was analysed from the parent rock saprolite weathering front to the upper fringe in the hillside and swamp system the chemistry of the wet atmospheric and throughfall deposits and the mengong waters was monitored in the nsimi watershed the carbon transfer occurs primarily in an organic form and essentially as colloids produced by the slow biodegradation of the swamp organic matter these organic colloids contribute significantly to the mobilization and transfer of fe al zr ti and th in the uppermost first meter of the swamp regolith when the organic colloid content is low i e in the hillside groundwater th and zr concentrations are extremely low 3 pmol l icp ms detection limits strongly insoluble secondary thorianite tho 2 and primary zircon zrsio 4 crystals control their mobilization respectively this finding thus justifies the potential use of both these elements as inert elements for isoelement mass balance calculations pertaining to the hillside regolith chloride can not be used as a conservative tracer of hydrological processes and chemical weathering in this watershed biogenic recycling significantly influences the low cl input fluxes sodium is a good tracer of chemical weathering in the watershed the sodium solute flux corrected from cyclic salt input was used to assess the chemical weathering rate even though low 2 8 mm kyr the chemical weathering rate predominates over the mechanical weathering rate 1 9 mm kyr compared to the rio icacos watershed the most studied tropical site the chemical weathering fluxes of silica and sodium in the mengong are 16 and 40 times lower respectively this is not only related to the protective role of the regolith thick in both cases but also to differences in the hydrological functioning this is to be taken into account in the calculations of the carbon cycle balance for large surfaces like that of the tropical forest ecosystems on a stable shield at the global level

influence of landslides on biophysical diversity a perspective from british columbia landslides have long been overlooked or underestimated as important natural disturbance agents in particular the ecological role of landslides in maintaining biological diversity has been largely ignored here we provide a western canadian british columbian perspective on the influences of landslides on biophysical diversity which is related in several ways to biological diversity we recognize several types of biophysical ecological diversity site diversity soil diversity and the derivative habitat or ecosystem including aquatic ecosystems diversity there are also a variety of landslide types depending on materials and on the rate and style of movement we discuss the roles of different landslide types on various aspects of terrestrial diversity landslides are simultaneously depositional and erosional processes that influence sites by redistributing materials and changing surface expression usually creating a complex microtopography that can include very dry ridges and hummocks and sometimes depressions with standing water landslide impacts to site also influence soil and soil development portions of landslides with exposed parent material are set back to the initial stages of soil development and ecological succession landslides can also change soil density structure porosity surface texture chemistry and microclimate by changing site and soil landslides also influence habitat landslides influence habitat diversity by engendering a mosaic of seral stages often both primary and secondary and in overwhelmingly forested landscapes often create nodes or hotspots of non forested habitat and biota in some areas like the boreal forest there is an important interplay between landslides and fire while on the coast of british columbia debris and snow avalanches can be the dominant disturbance agent low gradient and deep seated landslides are often opportunistically colonized by beaver and other water and shrub loving fauna sag ponds and impounded streams provide aquatic habitat often with standing dead trees landslide rubble and scarps provide denning nesting habitat escape terrain and cliff habitat for vertebrates

organic carbon export in the form of wood during an extreme tropical storm upper rio chagres panama widespread intense rainfall over the upper rio chagres watershed 414 km2 in central panama during december 2010 triggered numerous landslides that introduced large numbers of trees to the river network we flew by helicopter along the mainstem upper chagres and the adjacent margins of lake alhajuela into which the upper chagres flows in february and june 2011 we used low elevation video photography from these flights to tally the number of wood pieces stored along the lake margin and within the channel and the number of landslides reaching the mainstem we used these tallies with ground verified estimates of average wood piece size and landslide surface area and assumptions about wood density carbon content and aboveground biomass to develop a first order estimate of carbon export in the form of wood from the upper chagres following the 2010 storms based on the wood tally we estimate 9 6 to 16 mg c km2 export and from the landslide tally we estimate 24 mg c km2 we believe the landslide tally provides a more accurate minimum estimate of carbon export from the upper chagres during the december 2010 storms these values are an order of magnitude higher than limited data for average or background rates of wood based carbon export from other catchments but two orders of magnitude lower than wood based carbon export during extreme storms in taiwan the findings suggest that duration of flood flow above a threshold for mobilizing wood within the channel network exerts a more important control on wood export from the upper chagres than magnitude of flood peak copyright 2013 john wiley sons ltd

a kinematic model for the late cenozoic development of southern california crust and upper mantle a model is presented for the young and ongoing kinematic deformation of southern california crust and upper mantle that accounts for both the known late cenozoic geologic record and upper mantle structure in this model the high velocity upper mantle transverse ranges anomaly is created through the convergence and sinking of the entire thickness of subcrustal lithosphere using typical scaling relations we estimate this anomaly to be 500 c colder and 1 more dense than average southern california mantle of the same depth we infer that subcrustal lithosphere from both sides of the convergence zone participates nearly equally in the construction of the anomaly the low velocity upper mantle anomaly beneath the salton trough region is attributed to high temperatures and 1 4 partial melt related to adiabatic decompression during mantle upwelling our model has crustal motions in the central transverse ranges region differing from mantle motions while the subcrustal lithosphere south of the transverse ranges moves toward and sinks beneath the transverse ranges the corresponding crust largely avoids convergence by adopting a more westerly direction of motion the differing velocity fields necessitates of a decoupling zone immediately south of the transverse ranges near the moho we interpret the upper mantle anomalies as results of small scale convection beneath southern california to which we attribute much of the recent tectonic activity in the region