source parameters of acoustic emission events and scaling with mining induced seismicity a series of uniaxial compression tests were performed on 96 mm diameter quartzite samples 242 mm in length to understand the scaling of rock fracture processes nine acoustic emission ae sensors glued to each sample monitored the aes resulting from microcracking within the samples in contrast to previous ae studies the sensors were calibrated as velocity transducers so that the output could be compared to mining induced seismicity and natural earthquakes a new hybrid relative moment tensor method was applied to obtain source mechanism solutions for eight clusters of events once the ae rate accelerated prior to failure the event positions are associated with the observed failure planes the moment tensors were found to have double couple components indicating that shearing was occurring the stress drop appears to be constant over the range of moments suggesting the self similar scaling of the fracture response from the laboratory sample to mine seismicity and natural earthquakes over a wide range of length scales similar conclusions can be drawn by considering the apparent stress and source radius the scaling of the peak velocity and peak acceleration parameters is apparently consistent with mining induced seismicity but is considerably affected by high frequency attenuation and the limited bandwidth this is confirmed by the frequency magnitude plot which has a slope of unity the fracture processes in the laboratory are similar to those occurring underground near stope faces and pillars in deep level south african gold mines where there is a high vertical compression and low confinement

band limited heterogeneous fractal structure of earthquakes and acoustic emission events summary generalized correlation integral functions of the spatial distribution of earthquake epicentres have been determined for the chinese earthquake catalogue these correlation integral functions have three distinct power law regimes bands showing that the spatial distribution of earthquakes has band limited heterogeneous fractal structure we also found similar results in the hypocentre distribution of acoustic emission events in coarse grained granite under triaxial compression testing these results show that the fractal structure in rock fracturing is very complex they are heterogeneous in space and also band limited in scale the spatial distribution of fractures shows different patterns corresponding to different scale ranges microcracks in rock samples earthquake epicentres in seismic clusters seismic clusters along active fault zones boundary of crustal block for the most cases and active fault zones in the earth s crust the fractal dimension differs corresponding to the scale bands indicating there are some intrinsic characteristic scales existing in the fracturing system such as grain size and size of crustal blocks

impact of india asia collision on se asia the record in borneo abstract borneo occupies a central position in the sundaland promontory of se asia it has a complex cenozoic geological history of sedimentation and deformation which began at about the same time that india is commonly suggested to have started to collide with asia some tectonic reconstructions of east and se asia interpret a large se asian block with borneo at its centre which has been rotated clockwise and displaced southwards along major strike slip faults during the cenozoic due to the indentation of asia by india however the geological history of borneo is not consistent with the island simply forming part of a large block extruded from asia the large clockwise rotations and displacements predicted by the indentor model for borneo are incompatible with palaeomagnetic evidence and there is no evidence that the major strike slip faults of the asian mainland reach borneo seismic tomography shows there is a deep high velocity anomaly in the lower mantle beneath se asia interpreted as subducted lithosphere but it can be explained just as well by alternative tectonic models as by the indentor model very great thicknesses of cenozoic sediments are present in borneo and circum borneo basins and large amounts of sediment were transported to the crocker turbidite fan of north borneo from the eocene to the early miocene but all evidence indicates that these sediments were derived from local sources and not from distant sources in asia elevated by india asia collision the cenozoic geological history of borneo records subduction of the proto south china sea and miocene collision after this ocean lithosphere was eliminated and a variety of effects resulting from long term subduction beneath se asia there is little to indicate that india asia collision has influenced the cenozoic geological record in borneo

the hierarchical rupture process of a fault an experimental study abstract we describe the detailed faulting process of a naturally healed fault containing geometric and mechanical asperities in a granitic porphyry sample based on data collected with a high speed acoustic emission ae waveform recording system asperity failure is examined using the detailed spatio temporal distribution of ae hypocenters the initial phase of ae activity is also examined using high dynamic range waveforms our experimental results indicate that quasi static nucleation of the heterogeneous fault is associated with the failure of asperities on the fault plane the fracturing of an asperity is characterized by a dense spatial clustering of ae events and a changing b value b hereinafter which is manifest in three typical stages of failure as follows 1 foreshocks exhibiting a decrease in b 2 a period of mainshocks corresponding to a minimum in b and 3 aftershocks of increasing b the progressive fracture of several coupled asperities results in short term precursory fluctuations in both b and ae rate furthermore some ae events possess similar dynamic rupture features to those of earthquakes having an initial phase associated with the transition from quasi dynamic to dynamic rupture we conclude based on these experimental observations that fault rupture has hierarchical characteristics quasi static nucleation of fault rupture represents dynamic fracture of the asperities on the fault plane likewise a quasi static nucleation process characterized by dynamic microfracturing precedes the fracture of an asperity since dynamic motions are easier to detect remotely than static deformations understanding the hierarchical processes underlying fault rupture may thus be helpful for elucidating quasi static nucleation at larger scales in terms of the dynamic rupture of the asperities at smaller scales careful studies of asperity failure in the lab may guide future seismic studies of large asperities on natural faults potentially making it possible to recognize the final preparation stage before a large earthquake

seismic moment estimation based on fracture induced electromagnetic radiation abstract a new method to calculate the seismic moment based on electromagnetic radiation emitted during fracturing is presented results of this method for small fractures arising during the nucleation stages of an earthquake are shown to agree with former laboratory seismic measuring technique this method is quite easy to implement and can be used for measuring engineering failure intensity it can also be used to measure the seismic moment at the nucleation stages of an earthquake when seismic devices seismographs seismometers are not effective these measurements can then be used to calibrate the seismic devices for the estimation of the seismic moment during the catastrophic stages of earthquakes when these seismic devices are suitable and no electromagnetic radiation is present

a robust calibration technique for acoustic emission systems based on momentum transfer from a ball drop we describe a technique to estimate the seismic moment of acoustic emissions and other extremely small seismic events unlike previous calibration tech niques it does not require modeling of the wave propagation sensor response or signal conditioning rather this technique calibrates the recording system as a whole and uses a ball impact as a reference source or empirical green s function to correctly apply this technique we develop mathematical expressions that link the seismic mo ment m0 of internal seismic sources i e earthquakes and acoustic emissions to the impulse or change in momentum p of externally applied seismic sources i e me teor impacts or in this case ball impact we find that at low frequencies moment and impulse are linked by a constant which we call the force moment rate scale factor c f mm0 p this constant is equal to twice the speed of sound in the material from which the seismic sources were generated next we demonstrate the calibration technique on two different experimental rock mechanics facilities the first example is a saw cut cylindrical granite sample that is loaded in a triaxial apparatus at 40 mpa confining pressure the second example is a 2 m long fault cut in a granite sample and deformed in a large biaxial apparatus at lower stress levels using the empirical cali bration technique we are able to determine absolute source parameters including the seismic moment corner frequency stress drop and radiated energy of these magnitude 2 5 to 7 seismic events

origin and tectonic significance of the metamorphic rocks associated with the darvel bay ophiolite sabah malaysia banded hornblende gneiss foliated amphibolite hornblende chlorite and siliceous schist form lenses in an 8 km wide belt within the darvel bay ophiolite complex foliation in the belt is generally steep to vertical striking parallel to the trend of the belt and lineations are sub horizontal mineral and geochemical studies show that the metamorphic rocks represent banded and isotropic gabbros plagiogranites doleritic and basaltic dykes basaltic volcanics and cherts formed at a spreading ridge in a supra subduction zone environment which were deformed at high temperatures but low pressures along a transform fault incorporation of supracrustal cherts indicates that the transform extended for hundreds of kilometres between spreading centres garnet pyroxenites and amphibolites found as clasts in miocene volcanic agglomerates formed at high pressures and temperatures are interpreted as derived from a metamorphic sole underlying the complex formed during subduction of ocean crust and the emplacement of the ophiolite complex on sabah

empirical green s functions from small earthquakes a waveform study of locally recorded aftershocks of the 1971 san fernando earthquake seismograms from 52 aftershocks of the 1971 san fernando earthquake recorded at 25 stations distributed across the san fernando valley are examined to identify empirical green s functions and characterize the dependence of their waveforms on moment focal mechanism source and recording site spatial variations recording site geology and recorded frequency band recording distances ranged from 3 0 to 33 0 km hypocentral separations ranged from 0 22 to 28 4 km and recording site separations ranged from 0 185 to 24 2 km the recording site geologies are diorite gneiss marine and nonmarine sediments and alluvium of varying thicknesses waveforms of events with moment below about 1 5 1021 dyn cm are independent of the source time function and are termed empirical green s functions waveforms recorded at a particular station from events located within 1 0 to 3 0 km of each other depending upon site geology with very similar focal mechanism solutions are nearly identical for frequencies up to 10 hz there is no correlation to waveforms between recording sites at least 1 2 km apart and waveforms are clearly distinctive for two sites 0 185 km apart the geologic conditions of the recording site dominate the character of empirical green s functions even for source spatial separations of up to 20 0 km the empirical green s functions at a particular site are consistent in frequency content amplification and energy distribution therefore it is shown that empirical green s functions can be used to obtain site response functions the observations of empirical green s functions are used as a basis for developing the theory for using empirical green s functions in deconvolution for source pulses and synthesis of seismograms of larger earthquakes

tertiary stratigraphy and basin evolution southern sabah malaysian borneo abstract new mapping and dating of strata in the southern part of the central sabah basin in northern borneo has made it possible to revise the lithostratigraphy and chronostratigraphy of the area the recognition in the field of an early miocene regional unconformity which may be equivalent to the deep regional unconformity recognised offshore has allowed the development of a stratigraphic framework of groups and formations which correspond to stages in the sedimentary basin development of the area below the early miocene unconformity lies ophiolitic basement which is overlain by an accretionary complex of eocene age and a late paleogene deep water succession which formed in a fore arc basin the late paleogene deposits underwent syn depositional deformation including the development of extensive melanges all of which can be demonstrated to lie below the unconformity in this area some localised limestone deposition occurred during a period of uplift and erosion in the early miocene following which there was an influx of clastic sediments deposited in delta and pro deltaic environments in the middle miocene these deltaic to shallow marine deposits are now recognised as forming two coarsening upward successions mapped as the tanjong and kapilit formations the total thickness of these two formations in the central sabah basin amounts to 6000 m only half of the previous estimates although the total stratigraphic thickness of cenozoic clastic strata in sabah may be more than 20 000 m

a new view of integrating stratigraphic and tectonic analysis in south china sea and north borneo basins abstract this review outlines how se asian tectonic and stratigraphic studies could be more closely linked many tectonic papers on the region include comments on stratigraphic evidence and stratigraphic papers often allude to tectonic events but this paper highlights the benefits of a more detailed integration of the two fields of study into a single geological model by using inductive sequence stratigraphic methods supported by geohistory plots the south china sea and north borneo region has been traditionally been divided into provinces each with its own distinct stratigraphy a handicap in merging all the provinces into one geological model has been the inconsistent application of basic biostratigraphy and some examples are given that illustrate that more careful documentation of a complex data set is required in future work the inductive stratigraphic method requires increased analytical work to calibrate seismic data but even on current data an episodic stratigraphic history is indicated and a single tectono stratigraphic framework for the whole region is emerging with a greatly simplified and consistent terminology this review examines the impact of these methods on one important period of transition around the oligo miocene boundary the summary given for the oligo miocene transition questions the viability of the commonly cited slab pull tectonic model as both the historical order of geological events and geographic spread of effects does not fit that model as currently understood

shear failure of a granite pin traversing a sawcut fault abstract fault heterogeneities such as bumps bends and stepovers are commonly observed on natural faults but are challenging to recreate under controlled laboratory conditions we study deformation and microseismicity of a 76 mm diameter westerly granite cylinder with a sawcut fault with known frictional properties an idealized asperity is added by emplacing a precision ground 21 mm diameter solid granite dowel that crosses the center of the fault at right angles this intact granite pin provides a strength contrast that resists fault slip upon loading to 80 mpa in a triaxial machine we first observed a m 4 slip event that ruptured the sawcut fault slipped 40 m but was halted by the granite pin with continued loading the pin failed in a swarm of thousands of m 6 to m 8 events known as acoustic emissions aes once the pin was fractured to a critical point it permitted complete rupture events m 3 on the sawcut fault stick slip instabilities subsequent slip events were preceded by clusters of foreshock like aes all located on the fault plane and the spatial extent of the foreshock clusters is consistent with our estimate of a critical nucleation dimension h we also identified an aseismic zone on the fault plane surrounding the fractured rock pin a post mortem analysis of the sample showed a thick gouge layer where the pin intersected the fault suggesting that dilatancy of this gouge propped open the fault and prevented microseismic events in its vicinity recorded microseismicity separates into three categories slip on the sawcut fault fracture of the intact rock pin and off fault seismicity associated with pin related rock joints we found that pin fracture events were exclusively implosive anticrack even though the shear process zone was overall dilatant this shows how aseismic effects can lead to unexpected seismic manifestations of certain faulting processes

identifying fault heterogeneity through mapping spatial anomalies in acoustic emission statistics 1 seismicity clusters within fault zones can be connected to the structure geometric complexity and size of asperities which perturb and intensify the stress field in their periphery to gain further insight into fault mechanical processes we study stick slip sequences in an analog laboratory setting analysis of small scale fracture processes expressed by acoustic emissions aes provide the possibility to investigate how microseismicity is linked to fault heterogeneities and the occurrence of dynamic slip events the present work connects x ray computer tomography ct scans of faulted rock samples with spatial maps of b values slope of the frequency magnitude distribution seismic moments and event densities our current experimental setup facilitates the creation of a series of stick slips on one fault plane thus allowing us to document how individual stick slips can change the characteristics of ae event populations in connection to the evolution of the fault structure we found that geometric asperities identified in ct scan images were connected to regions of low b values increased event densities and moment release over multiple stick slip cycles our experiments underline several parallels between laboratory findings and studies of crustal seismicity for example that asperity regions in lab and field are connected to spatial b value anomalies these regions appear to play an important role in controlling the nucleation spots of dynamic slip events and crustal earthquakes

thrust tectonics along the north western continental margin of sabah borneo widely accepted plate tectonic models suggest that an inactive subduction zone lies along the north west continental margin of sabah in contrast interpretation of reflection seismic data acquired by bgr shows an autochthonous continental terrane comprising an oligocene to early miocene carbonate platform being progressively overthrust by an allochthonous rock complex progressive compression resulted in the development of four structural zones imbricated thrust sheets zone iii two thrust sheet systems one on top of the other zone iv a complex zone with multiphase deformation zone v and piercement ridges zone vi

an imbrication model for the rajang accretionary complex in sarawak borneo abstract the structural framework of the rajang accretionary complex is interpreted on the basis of field surveys conducted around the lupar fault zone in southwestern sarawak bedding dips in the rajang accretionary complex are generally southward while the complex as a whole becomes younger northward the complex is interpreted as a series of thrust slices formed by accretion at a subduction trench each slice forms a unit 10 to 15 km in width thrust slices of this order of this order of magnitude are consistent with those formed by accretion processes at modern subduction trenches it is suggested that accretion of late jurassic to cretaceous oceanic crust occurred initially from the pacific eastern side of borneo in the late cretaceous forming part of an arc system extending all along the eastern margin of asia from japan to kalimantan subsequently in the early tertiary due to bending of the southern end of the arc system in borneo the direction of subduction changed so that accretion occurred from the north

organic geochemical characteristics and depositional environment of the tertiary tanjong formation coals in the pinangah area onshore sabah malaysia article i nfo article history the tertiary tanjong formation coals exposed in the west middle block of the pinangah coalfield central part of southern sabah were analyzed and their depositional environments were interpreted the tertiary tanjong coals are humic and generally dominated by vitrinite with significant amounts of liptinite and low amounts of inertinite macerals total organic carbon contents toc of the coals range from 51 2 to 77 7 wt and yield of bitumen values ranging from 57 300 to 140 000 ppm which meet the standard as a source rock with good hydrocarbon generative potential in support good liquid hydrocarbons generation potential can be expected from the tanjong coals based on significant liptinitic content 15 this is supported by their high hydrogen index up to 300 mg hc g toc consistent with type ii and mixed type ii iii kerogens and py gc s2 pyrograms with n alkane alkene doublets extending beyond c30 the coal samples have vitrinite reflectance values in the range of 0 42 0 66 ro indicating immature to early mature stage for hydrocarbon generation these vitrinite reflectance values also indicated that the tanjong coals are with sub bituminous b a and high volatile bituminous c rank tmax values ranging from 419 to 451 c are good agreement with the vitrinite reflectance data this is supported by biomarker maturity parameters as suggested by the c32 homohopane the saturated fraction of the tanjong coals are characterized by dominant odd carbon numbered n alkanes n c23 to n c33 high pr ph ratios 8 18 high tm ts ratios 6 28 and pre dominant of regular sterane c29 all biomarker parameters clearly indicate that the organic matter was de rived from terrestrial inputs and deposited under oxic condition

a re assessment of age dating of fossiliferous limestones in eastern sabah borneo implications for understanding the origins of the indo pacific marine biodiversity hotspot abstract on the basis of a combined larger benthic foraminifera nannofossil and strontium isotope dating programme we confidently re assign muddy carbonate deposits from the lower kinabatangan river area of borneo to the oligocene rather than the early miocene high diversity coral rich 50 species deposits are here tightly constrained to predominately at or just after the early to late oligocene boundary larger benthic foraminifera zone te1 nannofossil zone np24 sr isotope ages 28 8 27 6 ma this new dating potentially pushes back the start of the indo west pacific centre of marine diversity at least for corals about 5 million years earlier than previous data indicated our new data supports maintaining separation of the muddy carbonates previously defined as the lower kinabatangan limestones haile wong 1965 from nearby crystalline limestones of the gomantong limestone formation dated here as early miocene larger benthic foraminifera zone te5 earliest tf1 sr isotope age 21 0 ma this apparently punctuated development of shallow marine carbonates is seen at several locations in northern borneo an area underlain by oceanic crust and long dominated by very deep marine sedimentation hutchison 2005 the opportunistic formation of clastic influenced coastal and isolated biohermal carbonates is both an important palaeontological data point and a geological marker of changing basin settings the new data on the first shallow marine deposits in a long established deep marine location and evidence for unconformities has important implications for the regional tectonic model in an area of hydrocarbon exploration

onland signatures of the palawan microcontinental block and philippine mobile belt collision and crustal growth process a review abstract the collision of the palawan microcontinental block with the philippine mobile belt had significantly influenced the geological evolution of the philippines multiple collisions involving several fragments through space and time resulted into the collage of terranes of varying origin exposed in this part of central philippines cusping of the overriding plate volcanic arc gap ophiolite emplacement incipient back arc rifting island rotation and tilting raised coastal terraces metamorphism intrusion of igneous rocks and steepened subducted slab as seen in focal mechanism solutions are some of the manifestations of this collision a late early miocene to early middle miocene age 20 16 ma is proposed for the major collision between the palawan indenter and the philippine mobile belt the collision boundary is located from the northern part of mindoro through the central mountain range swinging east of sibuyan island in the romblon island group and finally threading along the buruanga peninsula and eastern side of the antique ophiolite complex before exiting and connecting with the negros trench the collision through accretion and crustal thickening has contributed to the crustal growth of the philippine archipelago

premonitory acoustic emissions and stick slip in natural and smooth faulted westerly granite 1 a stick slip event was induced in a cylindrical sample of westerly granite containing a preexisting natural fault by loading at constant confining pressure of 150 mpa continuously recorded acoustic emission ae data and computer tomography ct generated images of the fault plane were combined to provide a detailed examination of microscale processes operating on the fault the dynamic stick slip event considered to be a laboratory analog of an earthquake generated an ultrasonic signal that was recorded as a large amplitude ae event first arrivals of this event were inverted to determine the nucleation site of slip which is associated with a geometric asperity on the fault surface ct images and ae locations suggest that a variety of asperities existed in the sample because of the intersection of branch or splay faults with the main fault this experiment is compared with a stick slip experiment on a sample prepared with a smooth artificial saw cut fault surface nearly a thousand times more ae were observed for the natural fault which has a higher friction coefficient 0 78 compared to 0 53 and larger shear stress drop 140 compared to 68 mpa however at the measured resolution the ultrasonic signal emitted during slip initiation does not vary significantly between the two experiments suggesting a similar dynamic rupture process we propose that the natural faulted sample under triaxial compression provides a good laboratory analogue for a field scale fault system in terms of the presence of asperities fault surface heterogeneity and interaction of branching faults

preslip and cascade processes initiating laboratory stick slip recent modeling studies have explored whether earthquakes begin with a large aseismic nucleation process or initiate dynamically from the rapid growth of a smaller instability in a cascade up process to explore such a case in the laboratory we study the initiation of dynamic rupture stick slip of a smooth saw cut fault in a 76 mm diameter cylindrical granite laboratory sample at 40 120 mpa confining pressure we use a high dynamic range recording system to directly compare the seismic waves radiated during the stick slip event to those radiated from tiny m 6 discrete seismic events commonly known as acoustic emissions aes that occur in the seconds prior to each large stick slip the seismic moments focal mechanisms locations and timing of the aes all contribute to our understanding of their mechanics and provide us with information about the stick slip nucleation process in a sequence of 10 stick slips the first few microseconds of the signals recorded from stick slip instabilities are nearly indistinguishable from those of premonitory aes in this sense it appears that each stick slip begins as an ae event that rapidly 20 s grows about 2 orders of magnitude in linear dimension and ruptures the entire 150 mm length of the simulated fault we also measure accelerating fault slip in the final seconds before stick slip we estimate that this slip is at least 98 aseismic and that it both weakens the fault and produces aes that will eventually cascade up to initiate the larger dynamic rupture

the age palaeoclimate palaeovegetation coal seam architecture mire types paleodepositional environments and thermal maturity of syn collision paralic coal from mukah sarawak malaysia abstract the mukah coal accumulated in the balingian formation where the time stratigraphic position is poorly defined by fauna though a probable late miocene age has always been assigned to this formation samples collected in the present study that yielded an abundance of casuarina pollen associated with occurrences of dacrydium stenochlaena palustris florschuetzia levipoli and also stenochlaena areolaris spores compare closely to zone pr9 of the palynological zonation of the malay basin and can be tied to depositional sequences of malay basin seismic sequences i2000 i3000 indicating an early miocene age for the studied coal the early miocene age shows that the mukah coal was formed during the collision between luconia block dangerous grounds with the borneo that lasted from late eocene to late early miocene the rapid increase of deposition base level caused by the collision is clearly reflected by the architecture of the mukah coal seams that were generally thin and also by the reverse order of the paleo peat bodies the studied coal samples contained large amounts of detrohuminite without the enrichment of liptinite group macerals usually explained by the dominance of herbaceous plants in the paleomires however the pollen assemblages recovered in the present study provide no support for a herbaceous swamp instead the peats were likely formed mainly from forest vegetation based on the recovery of dominant arboreal pollen assemblages in the present study palynomorph assemblages recovered in the present study with abundance of casuarina pollen associated with common occurrences of dacrydium strongly suggest kerangas vegetation and kerapah type peat swamps indicating a very wet climate the occurrence of rattan and pandanus pollens shows that the kerapah type peat swamps were locally bordered by rattan and pandanus swamps this shows that the prevailing use of coal petrography to discern the type of vegetation that was present in the peat forming mires may lead to wrong conclusions therefore a multi disciplinary approach must be applied for a more accurate and reliable spatial interpretation of the type of vegetation that was present in the peat forming mires consistent with the low sulphur content evidence from the palynomorph assemblages recovered from the coal seams shows that the coal forming peat was deposited in freshwater mires with little or no marine influence despite the fact that the accumulation of the mukah coal forming peat took place within a coastal plain setting moreover the fauna present in the host rock formation also suggested a brackish water environment of deposition

pulsed emplacement of the mount kinabalu granite northern borneo abstract high precision u pb ion microprobe analyses provide new constraints on the emplacement and origin of the kinabalu granite in sabah northern borneo the granite is a sheeted laccolith like body comprising dyke fed granitic units that young downwards each emplaced beneath the previous sheet analyses of concentric growth zones in zircons indicate crystallization between 7 85 0 08 and 7 22 0 07 ma and show that the entire pluton was emplaced and crystallized within less than 800 ka several pulses of magmatism are recognized each lasting for a maximum of 250 ka and possibly as briefly as 30 ka the oldest ages coincide with the highest elevations whereas the youngest ages are found at lower elevations around the edge of the body based on these new age data and field observations we identify the biotite granodiorite hornblende granite and porphyritic facies as the upper middle and lower units respectively inherited zircon ages indicate different protoliths for the upper and middle units the upper unit is derived from attenuated continental crust of the south china margin subducted beneath sabah the middle unit is sourced from melting of the crystalline basement in sabah with little or no contribution from south china crust supplementary material full u pb ion microprobe analytical data and modal and major element composition data are available at http www geolsoc org uk sup18385

laboratory generated m 6 earthquakes we consider whether mm scale earthquake like seismic events generated in laboratory experiments are consistent with our understanding of the physics of larger earthquakes this work focuses on a population of 48 very small shocks that are foreshocks and aftershocks of stick slip events occurring on a 2 0 m by 0 4 m simulated strike slip fault cut through a large granite sample unlike the larger stick slip events that rupture the entirety of the simulated fault the small foreshocks and aftershocks are contained events whose properties are controlled by the rigidity of the surrounding granite blocks rather than characteristics of the experimental apparatus the large size of the experimental apparatus high fidelity sensors rigorous treatment of wave propagation effects and in situ system calibration separates this study from traditional acoustic emission analyses and allows these sources to be studied with as much rigor as larger natural earthquakes the tiny events have short 3 6 s rise times and are well modeled by simple double couple focal mechanisms that are consistent with left lateral slip occurring on a mm scale patch of the precut fault surface the repeatability of the experiments indicates that they are the result of frictional processes on the simulated fault surface rather than grain crushing or fracture of fresh rock our waveform analysis shows no significant differences other than size between the m 7 to m 5 5 earthquakes reported here and larger natural earthquakes their source characteristics such as stress drop 1 10 mpa appear to be entirely consistent with earthquake scaling laws derived for larger earthquakes

dynamics and patterns of land levelling for agricultural reclamation of erosional badlands in chambal valley madhya pradesh india gully and badland erosion constitute important land degradation processes with severe on site and off site effects above all in sedimentary deposits and alluvial soils of the arid and semi arid regions agricultural use of the affected land is impeded both by the irreversible loss of topsoil and the morphological dissection of the terrain in various badland regions around the world a solution to the latter problem is attempted by infilling of gullies and levelling of badland topography in order restore a morphology suitable for agricultural cultivation gully and badland levelling for agricultural reclamation has been conducted for decades in the large ravine lands of india this study aims at analysing the distribution and dynamics of land levelling within the chambal badlands in morena district madhya pradesh between 1971 and 2015 using high to medium resolution satellite images from the corona landsat aster and rapideye missions and a multi temporal classification approach we have mapped and quantified areas that were newly levelled within eight observation periods we analysed the spatial relation of levelled land to several physical and socio economic factors that potentially influence the choice of reclamation site by employing geographic information system gis analysis methods and results from focus group discussions in selected villages results show that nearly 38 km2 or 23 of the badlands in the study area have been levelled within 45 years the levelling rate generally increases during the observation period but the annual variability is high we have found spatial relationships to badland morphology vicinity of existing cropland and proximity to villages and drainage lines from a socio economic point of view availability of financial and technical means access rights to the badland and ownership issues play an important role considering studies on soil degradation caused by levelling of badlands in other regions the sustainability of the newly reclaimed fields in the chambal badlands is questionable copyright 2017 john wiley sons ltd

source pulse enhancement by deconvolution of an empirical green s function observations of the earthquake source time function are enhanced if path recording site and instrument complexities can be removed from seismograms assuming that a small earthquake has a simple source its seismogram can be treated as an empirical green s function and deconvolved from the seismogram of a larger and or more complex earthquake by spectral division when the deconvolution is well posed the quotient spectrum represents the apparent source time function of the larger event this study shows that with high quality locally recorded earthquake data it is feasible to fourier transform the quotient and obtain a useful result in the time domain in practice the deconvolution can be stabilized by one of several simple techniques in this paper the method is implemented and tested on high quality digital recordings of aftershocks of the jan 9 1982 miramichi new brunswick earthquake in particular seismograms from a jan 17 aftershock 017 13 33 gmt local mag 3 5 exhibit path or site effects which complicate the determination of source parameters after deconvolution the apparent far field source of this event is a simple pulse in displacement with duration 0 07 second for both p and s

seismic energy release in mexican subduction zone earthquakes we estimated radiated seismic energy es from 18 shallow thrust mexican subduction zone earthquakes 4 1022 m 1 1 1028 dyne cm 11 h 37 km using digital accelerograms from the guerrero accelerograph array and neglecting stations with large site effects es is computed by integrating squared velocity spectra after applying geometrical spreading and q corrections we discarded epicentral recordings for the largest michoacan event we find that log es m 4 152 0 275 which gives a median value of es m and apparent stress a of 7 1 10 5 and 24 bars respectively the median es m value is in accordance with gutenberg and richter s g r 1956 formula for es in which es m 5 10 5 is implicit worldwide es m data where es is computed from local records mostly fall between 5 10 5 and 5 10 4 for events with m 1022 dyne cm on the other hand es m values generally lie between 5 10 6 and 5 10 5 if es is estimated from teleseismic records especially anomalous are the es m data from kikuchi and fukao 1988 for large and great earthquakes which fall near 5 10 6 thus while es from local data suggests that the g r relation seldom overestimates seismic energy release the teleseismic data point to the contrary the cause of this discrepancy may lie in the difficulty of resolving incoherent radiation from the fault and inappropriate choice of t in the analysis of teleseismic data

neogene sutures in eastern indonesia five suture zones are described from the zone of collision between the eurasian indian australian and pacific philippine sea plates within the eastern indonesia region these are the molucca sorong sulawesi banda and borneo sutures each of these sutures has a relatively short history compared to most pre neogene orogenic belts but each preserves a record of major changes in tectonics including subduction polarity reversals elimination of volcanic arcs changing plate boundaries and important extension within an overall contractional setting rapid tectonic changes have occurred within periods of less than 5 ma many of these events although important would be overlooked in older orogenic belts because the age resolution required to identify them even when the evidence is preserved is simply not possible q 2000 elsevier science ltd all rights reserved

source parameters of the 23 april 1992 m 6 1 joshua tree california earthquake and its aftershocks empirical green s function analysis of geos and terrascope data source parameters of the m 6 1 23 april 1992 joshua tree mainshock and 86 m 1 8 to 4 9 aftershocks are determined using an empirical green s function methodology for the aftershocks deconvolved p and s wave spectra are calculated for 126 pairs of closely spaced events recorded on portable geos stations s wave spectra from the two horizontal components are averaged the deconvolved spectra are fit by a ratio of omega square source models yielding an optimal least squares corner frequency for both the large and the small event in each pair we find no resolved difference between the inferred p and s wave corner frequencies using the standard brune model for stress drop we also find no resolved nonconstant scaling of stress drop with moment although we also conclude that detailed scaling systematics would be difficult to resolve in particular a weak increase of stress drop with moment over a limited moment magnitude cannot be ruled out for magnitudes smaller than m 3 to 3 5 the inferred stress drop values will be limited by the maximum observable corner frequency value of 60 hz for the mainshock source time functions are obtained from mainshock recordings at three terrascope stations pfo pas and gsc using an m 4 3 foreshock as an empirical green s function the results indicate a fairly simple single pulse source time function with clear south to north directivity and an inferred rupture radius of 5 to 6 km the deconvolved source time functions are inverted to obtain a finite rupture model that gives a robust estimate of rupture dimension early aftershocks are found to lie along the perimeters of regions with high mainshock slip the inferred mainshock stress drop value 56 bars is within the range determined for the aftershocks our derived mainshock source spectra do not show resolvable deviation from the omega square model

evidence for aseismic deformation rate changes prior to earthquakes abstractfor ten earthquakes in nonmagmatic settings there are credible published accounts of pre earthquake deformation rate changes lasting hundreds of seconds to more than a decade although most m 7 5 earthquakes have occurred without detectable pre earthquake deformation the detection threshold for aseismic deformation remains high in that aseismic slip with moment equivalent to an m5 earthquake would in most although not all cases have been missed interseismic deformation rates vary without being followed by earthquakes and a strain rate change prior to the 1989 mw6 9 loma prieta california earthquake is shown to be similar in size to many other rate changes that have occurred since that time most examples of pre earthquake aseismic deformation lasting hundreds of seconds or more probably originate adjacent to or downdip of the seismic rupture plane rather than within the zone that undergoes seismic failure

internal structure and emplacement mechanism of composite plutons evidence from mt kinabalu borneo the internal structure and emplacement mechanisms of composite plutons are investigated using new field data from the composite late miocene granitic intrusion of mt kinabalu in northern borneo the pluton was emplaced in the upper to middle crust in the late miocene at the contact between the ultramafic basement and sedimentary cover rocks structural data indicate that emplacement occurred during regional nnw sse oriented extension challenging tectonic models that involve contemporaneous regional compression the six major units forming the pluton were accommodated by upward flexure of the cover rocks with most magma pulses emplaced successively beneath their predecessors however the irregular 3d internal structure of the pluton also reflects preferential emplacement of successive units along the granite country rock contact of previous units in preference to the basement cover rock contact exploited by the initial units this study highlights the complex emplacement mechanisms and internal structure of composite intrusions and assesses how they differ from models of tabular emplacement

source analysis of acoustic emissions in aue granite cores under symmetric and asymmetric compressive loads the effect of stress anisotropy on the brittle failure of granite is investigated under uniaxial compression non standard asymmetric compression tests are performed on cores of aue granite diameter 52 mm length 100 mm in which 20 per cent of the core top surface remains unloaded the edge of the asymmetric steel loading plate acts as a stress concentrator from where a shear rupture is initiated the propagation of the fracture related process zone from top to bottom of the core is mapped by microcrack induced acoustic emissions compared to standard uniaxial tests with symmetric loading in the asymmetric tests both a greater quantity and more localized distributions of emission event hypocentres are observed the maximum event density doubles for asymmetric 20 events per 10 6 m3 compared to symmetric tests the cluster correlation coefficient a measure of strain localization in the faulting process reaches 0 15 for symmetric and 0 30 for asymmetric tests the clustering of events however is found post failure only three different amplitudes are used to determine b values discussed as a possible failure precursor focal amplitudes determined at a 10 mm source distance and maximum amplitudes measured at eight piezoceramic sensors lead to b values that drop before rock failure first pulse amplitudes automatically picked from emission wavelets show no anomaly first motion polarity statistics of amplitudes indicate that a shear crack type radiation pattern is responsible for 70 per cent of the failure of granite irrespective of stress boundary conditions for type s events with an equal percentage of dilatational and compressional first motions focal mechanisms are determined by fitting measured first pulse amplitudes to an assumed double couple radiation pattern while hypocentres of large type s events align parallel to the later fracture plane their fault plane solutions show no coherent pattern spatial views of fracture planes reconstructed from x ray computed tomograms reveal local small scale changes in fracture plane orientation nodal planes from average fault plane solutions of the microscopic acoustic emission events coincide with the overall orientation of the macroscopic fracture plane azimuth strike angle determined from thin sections and tomograms

a laboratory acoustic emission experiment under in situ conditions in this paper we revisit acoustic emission ae data from an in situ rock fracture experiment conducted at the underground research laboratory url in manitoba canada the mine by experiment a large scale excavation response test was undertaken at a depth of 420 m and involved the mechanical excavation of a cylindrical tunnel during the experiment a small array of 16 panametrics v103 ae sensors enclosed a 0 7 m 0 7 m 1 1 m rectangular prism of lac du bonnet granite located in the tunnel wall the v103 sensors were later calibrated in the laboratory and a source parameter analysis was undertaken using a spectral fitting method corner frequency and moment magnitude were found to be inside the ranges 250 khz fc 490 khz and 7 5 mw 6 8 respectively static stress drops ranged from 0 3 to 4 mpa which is consistent with large seismicity recorded at the url

radiated seismic energy from coda measurements and no scaling in apparent stress with seismic moment 1 the seismic coda consists of scattered waves that leave the earthquake source in a variety of directions the averaging of source radiation that results leads to stable ground motion spectra that we use as the basis for a robust measurement of radiated wave energy we apply an empirical green s function egf method to the seismic coda in order to investigate scaling of the radiated seismic energy we correct for path effects in the spectra of earthquakes by using a stack of closely located small earthquakes as an egf we apply this approach to four earthquake sequences in western north america that span a magnitude range from mw 3 0 mw 7 1 our estimates of scaled energy are consistent with independent measurements where available we find no dependence in individual seismic energy estimates on source station distance which validates the egf approximation we find that a constant scaled energy of 3 5 10 5 provides a reasonable fit to the data with no dependence of the scaled energy on seismic moment

observations of premonitory acoustic emission and slip nucleation during a stick slip experiment in smooth faulted westerly granite 1 to investigate laboratory earthquakes stick slip events were induced on a saw cut westerly granite sample by triaxial loading at 150 mpa confining pressure acoustic emissions ae were monitored using an innovative continuous waveform recorder the first motion of each stick slip was recorded as a large amplitude ae signal these events source locate onto the saw cut fault plane implying that they represent the nucleation sites of the dynamic failure stick slip events the precise location of nucleation varied between events and was probably controlled by heterogeneity of stress or surface conditions on the fault the initial nucleation diameter of each dynamic instability was inferred to be less than 3 mm a small number of ae were recorded prior to each macro slip event for the second and third slip events premonitory ae source mechanisms mimic the large scale fault plane geometry

a comparison of seismicity characteristics and fault structure between stick slip experiments and nature fault zones contain structural complexity on all scales this complexity influences fault mechanics including the dynamics of large earthquakes as well as the spatial and temporal distribution of small seismic events incomplete earthquake records unknown stresses and unresolved fault structures within the crust complicate a quantitative assessment of the parameters that control factors affecting seismicity to better understand the relationship between fault structure and seismicity we examined dynamic faulting under controlled conditions in the laboratory by creating saw cut guided natural fractures in cylindrical granite samples the resulting rough surfaces were triaxially loaded to produce a sequence of stick slip events during these experiments we monitored stress strain and seismic activity after the experiments fault structures were imaged in thin sections and using computer tomography the laboratory fault zones showed many structural characteristics observed in upper crustal faults including zones of localized slip embedded in a layer of fault gouge laboratory faults also exhibited a several millimeter wide damage zone with decreasing micro crack density at larger distances from the fault axis in addition to the structural similarities we also observed many similarities between our observed distribution of acoustic emissions aes and natural seismicity the aes followed the gutenberg richter and omori utsu relationships commonly used to describe natural seismicity moreover we observed a connection between along strike fault heterogeneity and variations of the gutenberg richter b value as suggested by natural seismicity studies areas of low b value marked the nucleation points of large slip events and were located at large asperities within the fault zone that were revealed by post experimental tomography scans our results emphasize the importance of stick slip experiments for the study of fault mechanics the direct correlation of acoustic activity with fault zone structure is a unique characteristic of our laboratory studies that has been impossible to observe in nature

structural styles in mesozoic and cenozoic melanges in the western cordillera of north america the term melange is currently used to describe several different kinds of mudstone rich rocks that are broadly characterized by an obscure stratigraphy stratal disruption or a chaotic block in matrix fabric four types of melange which can be defined in outcrop on the basis of mesoscopic fabric and lithologic composition are particularly widespread and distinctive type i includes sequences of originally interbedded sandstone and mudstone that record incipient to thorough disruption and fragmentation of strata accomplished largely by layer parallel extension type ii consists of similarly deformed thin layers of green tuff radiolarian ribbon chert and minor sandstone originally interbedded with black mudstone disruption in both types i and ii which probably occurred while the sediments were incompletely consolidated has been ascribed to either imbricate faulting in accretionary wedges or gravitationally driven deformation type iii comprises inclusions of diverse shapes sizes and compositions enveloped in a locally scaly pelitic matrix the ultimate source of fragments is obscure because the majority were not derived by either the progressive disruption of interbedded sediments or in situ tectonic plucking and abrasion of adjacent rocks although some type iii melanges may have originated deep within accretionary prisms final emplacement as olistostromes muddy debris flow deposits or mud diapirs seems likely type iii melanges are mechanically analogous to scaly sheared serpentinites many probably have been tectonically remobilized or even intruded into shallow level fault zones type iv consists of lenticular inclusions bounded by an anastomosing network of subparallel faults their fabric records progressive slicing in brittle fault zones each of the four types of melange described here could in theory have formed in a variety of settings on or within an accretionary wedge at an active convergent margin none can yet be singled out as a uniquely diagnostic subduction melange

soil and water losses from new citrus orchards growing on sloped soils in the western mediterranean basin ten representative research sites were selected in eastern spain to assess soil erosion rates and processes in new citrus orchards on sloping soils the experimental plots were located at representatives sites on limestone in areas with 498 to 715 mm year 1 mean annual rainfall north facing slopes herbicide treated and new less than 3 years old plantations ten rainfall simulation experiments 1 h at 55 mm h 1 on 0 25 m2 plots were carried out at each of the 10 selected study sites to determine the interill soil erosion and runoff rates the 100 rainfall simulation tests 10 10 m showed that ponding and runoff occurred in all the plots and quickly 121 and 195 s respectively following rainfall initiation runoff discharge was one third of the rainfall and sediment concentration reached 10 4 g l 1 the soil erosion rates were 2 4 mg ha 1 h 1 under 5 year return period rainfall thunderstorms these are among the highest soil erosion rates measured in the western mediterranean basin similar to badland mine spoil and road embankment land surfaces the positive relationship between runoff discharge and sediment concentration r2 0 83 shows that the sediment availability is very high soil erosion rates on new citrus orchards growing on sloped soils are neither tolerable nor sustainable copyright 2009 john wiley sons ltd

paleo oceanographic and tectonic settings of early miocene reefs and associated carbonates of offshore southeast asia the late oligocene to early middle miocene was a period of widespread reef and associated carbonate deposition over a wide latitudinal range in the offshore region of southeast asia a generally rising eustatic sea level during this period allowed the accumulation of thick reefal units an expansion of the coral algal regional facies belt north to japan and south to new zealand occurred during the early miocene as the result of a reduced oceanic latitudinal temperature gradient an episode of enhanced organic carbon burial is reflected in a positive dgr13c excursion from 17 5 to 13 5 ma increasing paleo oceanographic equability may have resulted in reduced ocean circulation with the resultant development of an expanded oxygen minimum zone marine oil prone or anic carbon was deposited in silled anoxic basins both bounded by and within island arc systems a combination of tectonic and paleo oceanographic factors therefore created conditions that favored contemporaneous deposition of organic carbon rich source beds and reef reservoirs during the latest early to early middle miocene paleogeographic and facies reconstructions for an 18 m y interval indicate that deposition occurred in three tectonic settings 1 passive continental margins 2 convergent plate boundaries and 3 obliquely convergent plate boundaries in all these settings the vertical motion histories of fault bounded blocks and of larger tectonic elements within which they are contained directly controlled the geographical distribution of carbonate buildups their scal and morphology duration diagenesis and relationship to siliciclastics

the impact of the farming practice of remodelling hillslope topography on badland morphology and soil erosion processes abstract badland landforms created in plio pleistocene clay landscapes of the basilicata region of southern italy form marginal features in a semi arid landscape dominated by the widespread cultivation of subsidised cereals these badland features are high relative relief forms exhibiting a high drainage density and steep slopes with slope angles typically in excess of 35 economic incentives to increase agricultural productivity have resulted in the practice of remodelling these marginal areas using heavy earth moving equipment remodelling the badland features creates longer slopes at lower angles which can be cultivated using conventional farm machinery these changes in hillslope morphology have altered the degree to which soil erosion processes operating in these areas are spatially coupled in the badland areas erosion and deposition are strongly localised with minimal sediment delivery to ephemeral or perennial channel systems the economically driven change in land use from visually striking badland areas to newly remodelled fields for agricultural use results in an increase in the coupling of drainage networks and a net increase in soil erosion

source parameters of picoseismicity recorded at mponeng deep gold mine south africa implications for scaling relations abstract we investigate the source parameters of picoseismic and nanoseismic events m w 4 1 recorded with a high sensitivity seismic network at the mponeng gold mine in south africa to gain new insights into the scaling of small seismic events the japanese german underground acoustic emission research in south africa jaguars network composed of one three component 3c accelerometer sensitivity 50 hz to 25 khz and 8 acoustic emission ae sensors sensitivity 1 khz to 180 khz is located at a depth of 3268 m and covers the limited volume of approximately 300 300 300 m the ae sensors are calibrated with respect to the 3c accelerometer in the frequency band 400 hz 17 khz the waveform data of two datasets are analyzed 1 the aftershock sequence of an m w 1 9 event that occurred approximately 30 m from our network and 2 the postblasting activity recorded during working days located at a distance 90 m from the network at the exploitation level for the analysis we applied spectral fitting and spectral ratio methods the calculated values of m w range from 0 8 down to 4 1 with corner frequencies 0 8 khz 13 6 khz source sizes from 8 cm to 1 3 m we observe static stress drops ranging from 1 mpa to 10 0 mpa with apparent stresses of 0 01 mpa 1 00 mpa stress drops are independent of the moment suggesting self similar behavior in the analyzed magnitude range 4 1 m w

a miocene collisional belt in north borneo uplift mechanism and isostatic adjustment quantified by thermochronology subduction followed by underthrusting of continental lithosphere driven by oligocene early miocene spreading in the south china sea marginal basin account for the tectonic features of sabah isostatic rebound then caused late miocene uplift of the western cordillera the strata were buried under 4 8 km of overburden then rapidly exhumed and cooled at 10 c ma 1 a rate of exhumation of 0 5 0 7 mm a 1 is deduced from thermochronology the same order of uplift in the labuk highlands has exposed metamorphic rocks of the epidote glaucophane facies rapid erosion of the western cordillera supplied abundant clastic sediments to the miocene pliocene baram delta oil bearing basin and to the eastern lowlands and sulu sea the eastern lowlands were affected by miocene rifting of the sulu sea marginal basin in contrast to the western cordillera the strata contain apatite crystals whose fission track ages pre date the containing rocks indicating burial by only about 2 3 km of overburden the terrain has been isostatically stable some apatite and all zircon crystals extracted from tertiary strata yield cretaceous fission track provenance ages

a new stratigraphy for the islands of the sumatran forearc indonesia abstract the sumatran forearc of western indonesia contains a number of islands where extensive exposures of basement rocks and their sedimentary cover may be examined the islands such as nias and the batu islands are located along the outer edge of the sumatran forearc whilst others including the banyak island group and pini island lie within the forearc basin detailed sedimentological palaeontological and palaeobathymetric data from the tertiary strata from the forearc region require a new stratigraphy as previous stratigraphic schemes have not explained the variations across the region adequately this stratigraphy developed initially from detailed data collected on nias and the banyak islands can fully account for the successions of sedimentary rocks on the banyak and batu islands and siberut and explains many of the apparent inconsistencies between previous stratigraphies a basement complex and six new formations are formally defined in this paper important sedimentological differences between these formations represent key stages in the evolution of the outer part of the sumatran forearc studies of the basement rocks across the forearc area suggest the basement is inhomogeneous large intact sections of ophiolitic material occur in some areas whilst there is evidence for both oceanic and continental basement in others such heterogeneity is to be expected in a long lived obliquely convergent margin in oligocene earliest miocene times extension of the heterogeneous basement is inferred through indirect evidence palaeobathymetric data from the oyo formation indicates that the initial deposition in the newly formed extensional sub basins on nias was in most areas deep marine in many cases below the ccd detailed biostratigraphic analyses and structural and geochronological studies indicate a major early miocene unconformity in the western lahewa sub basin and parts of central nias mujoi sub basin this unconformity was developed as a direct result of a period of basin inversion that affected western parts of nias whilst sub aerial erosion occurred in parts of western nias conformable deposition of the gawo and olodano formation continued in the gomo and eastern parts of the mujoi sub basins the shallow marine sedimentary rocks of the olodano formation tended to accumulate on intra sub basinal highs whose position was controlled by active faults that transected the sub basins the sedimentary record reveals that the lower and middle miocene phases of differential uplift and subsidence had ceased by the late miocene a massive influx of himalayan derived bengal fan sediments reached the sunda trench in the sumatra area in the late middle miocene continued addition of bengal fan material to the accretionary wedge south west of nias resulted in steady plate deflection and subsidence through flexural processes in forearc basin areas the flexural consequence of increased load added to the prism and associated subsidence history is documented by the sedimentary record on nias where the shallow marine olodano formation passes up into the neritic to upper bathyal lahomie formation the pliocene unconformity which is observed over all areas studied in the forearc is well constrained by structural biostratigraphic and sedimentological studies the unconformity represents the initiation of a major phase of uplift and deformation that continues to the present day rapid uplift of the outer arc ridge and deformation of the prism during the pliocene led to increased subsidence landward of the deformation the rapid subsidence of the forearc basin landward of the outer arc ridge has contributed greatly to the apparent differences between the forearc basin and the outer arc ridge at the present day two areas with remarkably similar pre pliocene histories now have remarkably different physiographies

growth of the maritime continent and its possible contribution to recurring ice ages the areal extent of the maritime continent the islands of indonesia and surrounding region has grown larger by 60 since 5 ma we argue that this growth might have altered global climate in two ways that would have contributed to making recurring ice ages possible first because rainfall over the islands of the maritime continent not only is heavier than that over the adjacent ocean but also correlates with the strength of the walker circulation the growth of the maritime continent since 5 ma may have contributed to the cooling of the eastern tropical pacific since that time scaling relationships between the strength of the walker circulation and rainfall over the islands of the maritime continent and between sea surface temperature sst of the eastern tropical pacific and the strength of easterly wind stress suggest that the increase in areal extent of islands would lead to a drop in that sst of 0 75 c although only a fraction of the 3 4 c decrease in ssts between the eastern and western tropical pacific the growth of the maritime continent may have strengthened the walker circulation increased the east west temperature gradient across the pacific and thereby enabled ice sheets to wax and wane over canada since 3 ma second because the weathering of basaltic rock under warm moist conditions extracts co2 from the atmosphere more rapidly than weathering of other rock or of basalt under cooler or drier conditions the increase in weathering due to increasing area of basalt in the maritime continent may have drawn down enough co2 from the atmosphere to affect global temperatures simple calculations suggest that increased weathering of basalt might have lowered global temperatures by 0 25 c possibly important for the overall cooling

normalized radiated seismic energy from laboratory fracture experiments on opalinus clayshale and barre granite we evaluate the radiated seismic energy normalized by external work for hydraulic fracturing beam bending and uniaxial compression experiments conducted on opalinus clayshale and barre granite specimens results suggest that normalized radiated seismic energy is highest for the beam bending followed by uniaxial compression and finally that the hydraulic fracturing experiments radiate the least seismic energy when normalized by external work we also find that the normalized radiated energy during tests on opalinus clayshale is 3 to 22 of that in barre granite across multiple loading mechanisms

contraction and extension in northern borneo driven by subduction rollback abstract during the paleogene the proto south china sea was subducted beneath northern borneo subduction ended with early miocene collision of the dangerous grounds reed bank north palawan block and the sabah cagayan arc much of northern borneo then became emergent forming the top crocker unconformity later in the early miocene subsidence resumed it is proposed that northward subduction of the celebes sea initiated formation of the sulu sea backarc basin followed by subduction rollback to the se this formed a volcanic arc which emerged briefly above sea level and collapsed in the middle miocene as rollback continued the sulu arc was active during middle and late miocene between sabah and the philippines rollback drove extension in northern borneo and palawan accompanied by elevation of mountains crustal melting and deformation offshore there were two important extensional episodes the first at about 16 ma is marked by the deep regional unconformity and the second at about 10 ma produced the shallow regional unconformity both episodes caused exhumation of deep crust probably on low angle detachments and were followed by granite magmatism the nw borneo palawan trough and offshore sabah fold and thrust belt are often interpreted as features resulting from collision regional compression or subduction however there is no seismicity dipping slab or volcanicity indicating subduction nor obvious causes of compression the trough developed after the middle miocene and is not the position of the paleogene trench nor the site of neogene subduction inboard of the trough is a thick sediment wedge composed of an external fold and thrust belt and internal extensional zone with structures broadly parallel to the trough the trough is interpreted as a flexural response to gravity driven deformation of the sediment wedge caused by uplift on land that resulted from extension with a contribution of deep crustal flow

gully head erosion processes on a semi arid valley floor in kenya a case study into temporal variation and sediment budgeting a three year monitoring programme of gully head retreat was established to assess the significance of sediment production in a drainage network that expanded rapidly by gully head erosion on the low angled alluvio lacustrine njemps flats in semi arid baringo district kenya this paper discusses the factors controlling the large observed spatial and temporal variation in gully head retreat rates ranging from 0 to 15 m a 1 the selected gullies differed in planform and in runoff contributing catchment area but soil material and land use were similar the data were analysed at event and annual timescales the results show that at annual timescale rainfall amount appears to be a good indicator of gully head retreat while at storm event timescale rainfall distribution has to be taken into account a model is proposed including only rainfall p and the number of dry days dd between storms which explains 56 per cent of the variation in retreat rate of the single headed gully of lam1 a detailed sediment budget has been established for lam1 and its runoff contributing area rca by measuring sediment input from the rca the sediment output by channelized flow and linear retreat of the gully head for nine storms it can be seen that erosion shifts between different components of the budget depending on the duration of the dry period dd between storms sediment input from the rca was usually the largest component for the smaller storms the erosion of the gully head occurred as a direct effect of runoff falling over the edge ghwaterfall and of the indirect destabilization of the adjacent walls by the waterfall erosion and by saturation ghmass storage the latter component ghmass storage was usually much larger that the former ghwaterfall the sediment output from the gully was strongly related to the runoff volume while the linear retreat because of its complex behaviour was not overall the results show that the annual retreat is the optimal timescale to predict retreat patterns more detailed knowledge about relevant processes and interactions is necessary if gully head erosion is to be included in event based soil erosion models copyright 2001 john wiley sons ltd

foreshocks during the nucleation of stick slip instability 1 we report on laboratory experiments which investigate interactions between aseismic slip stress changes and seismicity on a critically stressed fault during the nucleation of stick slip instability we monitor quasi static and dynamic changes in local shear stress and fault slip with arrays of gages deployed along a simulated strike slip fault 2 m long and 0 4 m deep in a saw cut sample of sierra white granite with 14 piezoelectric sensors we simultaneously monitor seismic signals produced during the nucleation phase and subsequent dynamic rupture we observe localized aseismic fault slip in an approximately meter sized zone in the center of the fault while the ends of the fault remain locked clusters of high frequency foreshocks mw 6 5 to 5 0 can occur in this slowly slipping zone 5 50 ms prior to the initiation of dynamic rupture their occurrence appears to be dependent on the rate at which local shear stress is applied to the fault the meter sized nucleation zone is generally consistent with theoretical estimates but source radii of the foreshocks 2 to 70 mm are 1 to 2 orders of magnitude smaller than the theoretical minimum length scale over which earthquake nucleation can occur we propose that frictional stability and the transition between seismic and aseismic slip are modulated by local stressing rate and that fault sections which would typically slip aseismically may radiate seismic waves if they are rapidly stressed fault behavior of this type may provide physical insight into the mechanics of foreshocks tremor repeating earthquake sequences and a minimum earthquake source dimension

discussion of a miocene collisional belt in north borneo uplift mechanism and isostatic adjustment quantified by thermochronology scientific editing by alex maltman john milsom robert holt write knowledge of the gravity field is vital to any study of isostasy this was acknowledged by hutchison et al 2000 when they noted that the work of holt 1998 placed constraints on their geological model for sabah however they went on to ignore these constraints arguing that the depth of the crustal root beneath the western cordillera might have been overestimated due to the model assumption of an excessively thick ophiolitic basement and that the presence of thick crust beneath sabah was in conflict with the outcropping geology the hutchison et al interpretations of the deep structure of sabah were illustrated in a series of cross sections in which some features notably the topography were amplified for the sake of clarity there was however no suggestion that any features would be underemphasized and the depth scales although described as only rough guides indicated normal 5 10 km thicknesses for oceanic crust therefore and in the light of the comments quoted above the thin crust shown throughout sabah and the generally somewhat greater thickness of the extended continental crust of the dangerous grounds must be regarded as essential elements of the model the late miocene cross section fig 1 showing the end of orogeny in sabah is a guide to the hutchison et al view of the present day situation crust is less than 30 km thick beneath the western cordillera and less than 20 km thick elsewhere we contend that these values are incompatible with the gravity field and that it is no more acceptable to present a geological interpretation that ignores geophysical data than a geophysical interpretation that ignores geology some way must be found of reconciling the two fig 1 sabah in the late miocene from hutchison et al 2000 fig 6b

neogene arc continent collision in sabah northern borneo malaysia abstract the neogene evolution of sabah can be interpreted in terms of an arc continent collision initiated during early middle miocene time and followed by intraplate shortening the latter being active in this area at the present day the volcanic arc of late oligocene middle miocene age is imbricated with melanges and thrust northwestward on a polyphase deformed turbiditic sequence of late cretaceous middle miocene age crocker range intraplate shortening is seen in the thrusting and folding offshore sabah along the palawan north borneo trench and also by broad open folds and strike slip faulting in the previously sutured terranes this collision can either be interpreted as the final stage of southward subduction of the hypothetical proto south china sea or the result of back thrusting of the sulu volcanic arc resulting from the subduction of the celebes sea toward the north

geological development of the central and south vietnamese margin implications for the establishment of the south china sea indochinese escape tectonics and cenozoic volcanism abstract the vietnamese margin forms a key region to the understanding of escape tectonics and the development of the south china sea scs the existing geological reconstructions of the region are restricted to studies of single basins are based on limited amounts of geophysical data or analysis of onshore geological features these models are critically assessed on the basis of interpretation of the most comprehensive 2 d digital seismic database published to date within the area combined with a thorough analysis of existing literature and a new model is presented the vietnamese margin is underlain by a series of paleogene rift basins established through southeastward extrusion of indochina the east vietnam boundary fault evbf forms the almost 1000 km long seaward continuation of the left lateral ailao shan red river shear zone asrrsz toward the southern half of the phu khanh basin the evbf breaks up into discrete segments and splays into the se directed tua hoa fault zone paleogene faults splayed from the evbf and the mae ping shear zone and accommodated the coeval motion of these two major left lateral structural lineaments during the late oligocene basin inversions offshore occurred contemporaneously with initial right lateral inversion along the mae ping shear zone and the onset of major uplift of the metamorphic core complexes along the asrrsz it is suggested that a dramatic change of the regional stress pattern occurred in response to the northward movement of india and the effective coupling of the west burma block and india the later resulting in broadening of the indenting continental mass after the mid oligocene left lateral movements across the offshore evbf decreased and eventually ceased later onshore sinistral movements were accommodated by internal shortening and local clockwise block rotations within the shan thai terrain renewed rifting offshore south vietnam resulted from the jump of the scs spreading axis and subsequent neogene southwestward propagation of continental break up the neogene opening of the scs is viewed as a consequence of a slab pull associated with subduction of the proto scs underneath borneo as offshore neogene escape tectonism had virtually ceased during this phase of rifting right lateral transtension is inferred along n to nw oriented fault zones in the phu khanh and the nam con son basins rifting and by inference seafloor spreading continued until the end of middle miocene time although at significantly reduced rates during the final 5 10 ma termination of seafloor spreading is marked by a distinct latest middle miocene unconformity in the nam con son and the southern phu khanh basins neogene volcanism resulted in the build up of several magmatic structures across the central and south vietnamese margin and induced reactivation of older faults in the phu khanh basin the offshore magmatism heralded widespread volcanism onshore southern indochina associated with a latest neogene uplift and denudation event the uplift led to significantly increased siliciclastic accumulation rates offshore which repressed widespread carbonate deposition

slow and fast ruptures on a laboratory fault controlled by loading characteristics recent geodetic observations indicate that a single fault may slip slowly and silently or fast and seismically in different circumstances we report laboratory experiments that demonstrate how the mode of faulting can alternate between fast stick slip events 70 to 500 mm s sliding rates and slow silent events 0 001 to 30 mm s as a result of loading conditions rather than friction properties or stiffness of the loading machine the 760 mm long granite sample is close to the critical nucleation length scale for unstable slip so small variations in nucleation properties result in measurable differences in slip events slow events occur when instability cannot fully nucleate before reaching the sample ends dynamic events occur after long healing times or abrupt increases in loading rate which suggests that these factors shrink the spatial and temporal extents of the nucleation zone arrays of slip strain and ground motion sensors installed on the sample allow us to quantify seismic coupling and study details of premonitory slip and afterslip we find that seismic coupling decreases when slip rates fall below about 70 mm s the slow slip events we observe are primarily aseismic less than 1 of the seismic coupling of faster events and produce swarms of very small m 6 to m 8 events these mechanical and seismic interactions suggest that faults with transitional behavior where creep small earthquakes and tremor are often observed could become seismically coupled if loaded rapidly either by a slow slip front or dynamic rupture of an earthquake that nucleated elsewhere

the geology of northern sabah malaysia its relationship to the opening of the south china sea basin abstract the northern part of sabah consisting of sedimentary and igneous rocks of early cretaceous to pliocene age has experienced three major episodes of deformation associated with nw se and n s oriented compressions the earliest episode deformed and uplifted an oceanic basement chert spilite formation to form an elongate basin trending approximately ne sw during the late cretaceous to early eocene this elongate basin became the site for the deposition of middle eocene to early miocene quartzose sediments of the crocker and kudat formations sourced from continental basement towards the southwest and north respectively these sediments were subsequently deformed by a second episode of deformation associated with nw se and n s oriented compressions during the latter part of the late oligocene and the early middle miocene to form a series of imbricate thrust slices the n s trending compressive direction controlled the development of approximately e w trending basins during the deposition of the upper miocene sediments of the south banggi and bongaya formations the continuation of n s compression which represents the third episode of deformation gently deformed these sediments the three episodes of deformation were related to the differential southward movements of continental blocks separated from the southern margin of china during the intermittent opening of the south china sea subbasins the first episode was related to the opening of the southwest subbasin while the second episode was related to both the opening of the southwest and east subbasins the third episode was related to continued opening in the east subbasins

alluvial gully erosion an example from the mitchell fluvial megafan queensland australia considerable attention has been focused on the role of gullies as a contributor to contemporary sediment loads of rivers in australia in southern australia rapid acceleration of hillslope gully erosion has been widely documented in the post european period last 200 years in the northern australian tropics however gully erosion processes operating along alluvial plains have not been well documented and can differ substantially from those gullies eroding into colluvium on hillslopes aerial reconnaissance surveys in 2004 along 13 500 km of the main stem rivers that drain into the gulf of carpentaria goc identified extensive areas of alluvial lands that have been impacted by a pervasive form of gully erosion more detailed remote sensing based mapping within the 31 000 km2 mitchell river fluvial megafan has identified that active gullying into alluvium occupies 0 4 129 km2 of the lower mitchell catchment these alluvial gullies are concentrated along main drainage channels and their scarp heights are highly correlated to the local relief between the floodplain and river thalweg while river incision into the megafan since the pleistocene has developed the relief potential for erosion other factors such as floodplain hydrology soil dispersibility and vegetation also influence the distribution of gullies in this paper we present a conceptual model of alluvial gullies and contend that they represent a distinct end member in the continuum of gully forms that have been described in the geomorphic literature an understanding of the processes driving this form of alluvial gullying can only be gained when they are differentiated from widely described colluvial hillslope gully models and theories we present evidence of type examples of alluvial gullying in the mitchell and through analysis of their distribution and morphology at different scales highlight some of the key mechanisms that are potentially initiating these features and driving their expansion copyright 2009 john wiley sons ltd

depositional history of the sulu sea from odp sites 768 769 and 771 holes were drilled at three sites in the sulu sea on ocean drilling program leg 124 site 768 lies in the deeper part of the se sub basin and sites 769 and 771 lie on the flanks of the cagayan ridge the results indicate that the sulu basin originated in the late early miocene c 18 8 ma in a backarc setting the cagayan ridge was a site of early to early middle miocene arc volcanism with the deposition of a thick sequence of andesitic to basaltic volcaniclastic deposits in the basin center an early miocene pelagic sequence is interrupted by a thick unit of rhyolitic to dacitic pyroclastic flows middle to late miocene sedimentation is more continental in character with thick quartz rich turbidites in the basin center only the hemipelagic claystone related to these terrigenous turbidites were deposited on the cagayan ridge a decrease in the supply of clastic detritus from arc and continental sources and a change in the level of the carbonate compensation depth in the upper pliocene resulted in pelagic carbonate deposition throughout the late pliocene and pleistocene

determination of rupture duration and stress drop for earthquakes in southern california a simple technique is developed for determining the rupture duration and stress drop of earthquakes between magnitudes 3 5 and 4 0 using the time between the p wave onset and the first zero crossing 1 2 on seismograms from local seismic networks this method is applied to 10 main shocks in southern california to investigate regional variations in stress drop the initial pulse widths of 65 foreshocks or aftershocks of these events were measured values of 1 2 for small earthquakes below about magnitude 2 2 are generally observed to remain constant with decreasing magnitude in four sequences studied the relative pulse width of a particular main shock m 3 5 at a given station is found to be correlated with the relative pulse width of its aftershocks recorded at that station these observations are interpreted to signify that the waveforms of these small events m 2 2 are essentially the impulse response of the path between the source and receiver values of 1 2 determined from small foreshocks and aftershocks are therefore subtracted in effect deconvolved from those of each main shock to obtain an estimate of the rupture duration of the main shock which is corrected for path effects significant variations in rupture duration and stress drop are observed for the main shocks studied aftershock locations and azimuthal variations in 1 2 both indicate that the rupture zone of one earthquake expanded unilaterally a factor of 10 variation in stress drop is calculated for two adjacent events of similar seismic moments occurring 1 hr apart on the san jacinto fault system the first event in this pair had the highest stress drop of the events studied 860 bars and was followed within 8 months by a magnitude 5 5 earthquake 2 km away

hydrocarbon source potential of eocene miocene sequence of western sabah malaysia abstract an evaluation of the petroleum generating potential of onshore eocene miocene sequences of western sabah malaysia was performed based on organic petrological and geochemical methods the sequences analysed are the belait meligan temburong and west crocker formations of western sabah the belait formation which is stage iv equivalent in the offshore represents one of the major source rock reservoirs of the petroleum bearing sabah basin the eocene early miocene west crocker and temburong formations are deepwater turbidites whilst the miocene meligan and belait formations are shallow marine fluvio deltaic deposits the vitrinite reflectance and pyrolysis t max values show that the belait samples are generally immature for hydrocarbon generation whereas the meligan temburong and west crocker samples are in the mature to late maturity stage of hydrocarbon generation the overall bulk source rock properties of the belait and meligan show fair to good petroleum source rock potential with toc more than 1 wt hydrocarbon yield in the range of 400 1300 ppm and moderately high hi for many of the samples most of the samples representing the temburong and west crocker formations have toc less than 1 wt and have no to fair hydrocarbon generating potential interestingly the samples collected in the west crocker formation characterized by slump deposits mtd have toc 2 and possess good to excellent hydrocarbon generating potential the organic matter present in all of the studied formations is mainly of terrigenous origin based on the abundance of woody plant materials observed under the microscope consequently the analysed sequences are predominantly gas prone dominated by type iii and type iii iv kerogen except for minor occurrence of mixed oil gas prone type ii iii kerogen in the belait formation and in the slump mass transport deposits mtd of the west crocker formation

large nucleation before large earthquakes is sometimes skipped due to cascade up implications from a rate and state simulation of faults with hierarchical asperities 1 does a large earthquake have a large quasi static preparation a hierarchical asperity model in which a large tough patch patch l contains smaller fragile patches patch s enables a large earthquake to start with only small preparation because of cascade up rupture growth we realized such a model in a rate and state framework by heterogeneous distributions of the state evolution distance and its consequences are investigated by earthquake sequence simulations focus is put on elementary processes the interaction between two scales one patch l containing one patch s is simulated with their size ratio as a parameter if patch s is larger than the nucleation size of patch l the system falls into a limit cycle consisting of only one earthquake that starts with patch s nucleation and grows dynamically to rupture entire patch l if patch s is considerably smaller than the nucleation size of patch l small earthquakes never dynamically cascade up and the large earthquakes are initiated by large quasi static nucleation in between large earthquakes start in various ways by large nucleation dynamic cascade up or delayed cascade up in the final stage of quasi static nucleation the preseismic moment release rate increases roughly inversely proportional to the time to failure tf with its amplitude depending on the nucleation size for a patch s rupture to cascade up strength in the adjacent region must have been reduced manifested by a higher creep velocity before the patch s nucleation starts following 1 tf acceleration large nucleation sometimes has a precursory small earthquake characterized by larger afterslip than nonprecursory ones