the earthquake prediction experiment at parkfield california since 1985 a focused earthquake prediction experiment has been in progress along the san andreas fault near the town of parkfield in central california parkfield has experienced six moderate earthquakes since 1857 at average intervals of 22 years the most recent a magnitude 6 event in 1966 the probability of another moderate earthquake soon appears high but studies assigning it a 95 chance of occurring before 1993 now appear to have been over simplified the identification of a parkfield fault segment was initially based on geometric features in the surface trace of the san andreas fault but more recent microearthquake studies have demonstrated that those features do not extend to seismogenic depths on the other hand geodetic measurements are consistent with the existence of a locked patch on the fault beneath parkfield that has presently accumulated a slip deficit equal to the slip in the 1966 earthquake a magnitude 4 7 earthquake in october 1992 brought the parkfield experiment to its highest level of alert with a 72 hour public warning that there was a 37 chance of a magnitude 6 event however this warning proved to be a false alarm most data collected at parkfield indicate that strain is accumulating at a constant rate on this part of the san andreas fault but some interesting departures from this behavior have been recorded here we outline the scientific arguments bearing on when the next parkfield earthquake is likely to occur and summarize geophysical observations to date

aseismic slip during the 1996 earthquake swarm in and around the onikobe geothermal area ne japan abstract in august 1996 an earthquake swarm including 4 earthquakes of magnitudes greater than 5 occurred in and around the onikobe geothermal area northeast japan while earlier studies detected ground displacements by l band jers radar interferograms there remained certain puzzling discrepancies between the observations and the predictions from a seismologically inferred model and no satisfactory models have yet been proposed here by identifying that a steep gradient in the radar line of sight changes exists in seismicity gaps to the east and west of the torage area just to the north of the onikobe caldera we propose two aseismic reverse faults which turn out to contribute to a local topographic growth as well as explaining the pre existing discrepancies another significant signal is detected in a region in which no large earthquakes occurred we account for this signal by another aseismic fault this fault adds to another evidence for the recent hypothesis that aseismic fault motion drives earthquake swarm

surface deformation and coherence measurements of kilauea volcano hawaii from sir c radar interferometry the shuttle imaging radar c x synthetic aperture radar sir c x sar radar on board the space shuttle endeavor imaged kilauea volcano hawaii in april and october 1994 for the purpose of measuring active surface deformation by the methods of repeat pass differential radar interferometry observations at 24 cm l band and 5 6 cm c band wavelengths were reduced to interferograms showing apparent surface deformation over the 6 month interval and over a succession of 1 day intervals in october a statistically significant local phase signature in the 6 month interferogram is coincident with the pu u o o lava vent interpreted as deformation the signal implies centimeter scale deflation in an area several kilometers wide surrounding the vent peak deflation is roughly 14 cm if the deformation is purely vertical centered southward of the pu u o o caldera delays in the radar signal phase induced by atmospheric refractivity anomalies introduce spurious apparent deformation signatures at the level of 12 cm peak to peak in the radar line of sight direction though the phase observations are suggestive of the wide area deformation measured by global positioning system gps methods the atmospheric effects are large enough to limit the interpretation of the result it is difficult to characterize centimeter scale deformations spatially distributed over tens of kilometers using differential interferometry without supporting simultaneous spatially distributed measurements of refractivity along the radar line of sight studies of the interferometric correlation of images acquired at different times show that l band is far superior to c band in the vegetated areas even when the observations are separated by only 1 day these results imply longer wavelength instruments are more appropriate for studying surfaces by repeat pass observations

detection of a locked zone at depth on the parkfield california segment of the san andreas fault the parkfield california segment of the san andreas fault is transitional in character between the creeping segment of the fault to the northwest and the locked carrizo plain segment to the southeast the rate of shallow fault slip decreases from 25 30 mm yr northwest of the epicenter of the 1966 parkfield earthquake to zero at the southeastern end of the 1966 rupture zone data from a network of trilateration lines spanning the san andreas fault near parkfield and extending to the pacific coast near san luis obispo shed light on the rate of fault slip at depth since the 1966 earthquake in this study average rates of line length change and shallow fault slip were inverted to determine the slip rate at depth on the parkfield fault segment the fault is taken to be a vertical surface with unknown distribution of strike slip displacement in an elastic half space a striking result of the inversions is that all solutions providing acceptable fits to the data exhibit a locked zone essentially coincident with the rupture surface of the 1966 parkfield earthquake the data require that the locked zone extend nearly as far north as the 1966 epicenter however the vertical extent of the locked zone is not well resolved over much of the parkfield segment the fault is slipping faster at the earth s surface than it is at seismogenic depths in order to fit the trilateration measurements it is necessary to include a component of contraction normal to the trend of the san andreas the inversion results suggest a spatially uniform normal strain of 0 06 strain yr the orientation of the contraction is compatible with geologic and seismic evidence of active folding and reverse faulting in the region the magnitude of the contraction is consistent with convergence rates inferred from global plate motion models

the displacement field of the landers earthquake mapped by radar interferometry geodetic data obtained by ground or space based techniques can be used to infer the distribution of slip on a fault that has ruptured in an earthquake although most geodetic techniques require a surveyed network to be in place before the earthquake1 3 satellite images when collected at regular intervals can capture co seismic displacements without advance knowledge of the earthquake s location synthetic aperture radar sar interferometry first introduced4 in 1974 for topographic mapping5 8 can also be used to detect changes in the ground surface by removing the signal from the topography9 10 here we use sar interferometry to capture the movements produced by the 1992 earthquake in landers california11 we construct an interferogram by combining topographic information with sar images obtained by the ers 1 satellite before and after the earthquake the observed changes in range from the ground surface to the satellite agree well with the slip measured in the field with the displacements measured by surveying and with the results of an elastic dislocation model as a geodetic tool the sar interferogram provides a denser spatial sampling 100 m per pixel than surveying methods1 3 and a better precision 3 cm than previous space imaging techniques12 13

atmospheric effects in interferometric synthetic aperture radar surface deformation and topographic maps interferogram images derived from repeat pass spaceborne synthetic aperture radar systems exhibit artifacts due to the time and space variations of atmospheric water vapor other tropospheric variations such as pressure and temperature also induce distortions but the effects are smaller in magnitude and more evenly distributed throughout the interferogram than the wet troposphere term spatial and temporal changes of 20 in relative humidity lead to 10 cm errors in deformation products and perhaps 100 m of error in derived topographic maps for those pass pairs with unfavorable baseline geometries in wet regions such as hawaii these are by far the dominant errors in the spaceborne imaging radar c and x band synthetic aperature radar sir c x sar interferometric products the unknown time delay from tropospheric distortion is independent of frequency and thus multiwavelength measurements such as those commonly used to correct radar altimeter and global positioning system gps ionospheric biases cannot be used to rectify the error in the topographic case the errors may be mitigated by choosing interferometric pairs with relatively long baselines as the error amplitude is inversely proportional to the perpendicular component of the interferometer baseline for the sir c x sar hawaii data we found that the best longest baseline pair produced a map supporting 100 m contouring whereas the poorest baseline choice yielded an extremely noisy topographic map even at this coarse contour interval in the case of deformation map errors the result is either independent of baseline parameters or else very nearly so here the only solution is averaging of independent interferograms so in order to create accurate deformation products in wet regions many multiple passes may be required rules for designing optimal data acquisition and processing sequences for interferometric analyses in nondesert parts of the world are 1 to use the longest radar wavelengths possible within ionospheric scintillation and faraday rotation limits 2 for topography maximize interferometer baseline within decorrelation limits and 3 for surface deformation use multiple observations and average the derived products following the above recipe yields accuracies of 10 m for digital elevation models and 1 cm for deformation maps even in very wet regions such as hawaii

surface and sub surface multi proxy reconstruction of middle to late holocene palaeoceanographic changes in disko bugt west greenland we present new surface water proxy records of meltwater production alkenone derived relative sea surface temperature diatom alkenones and sea ice diatoms changes from the disko bugt area off central west greenland we combine these new surface water reconstructions with published proxy records benthic foraminifera bottom water proxy dinocyst assemblages surface water proxy along with atmospheric temperature from greenland ice core and greenland lake records this multi proxy approach allows us to reconstruct centennial scale middle to late holocene palaeoenvironmental evolution of disko bugt and the western greenland coastal region with more detail than previously available combining surface and bottom water proxies identifies the coupling between ocean circulation west greenland current conditions the atmosphere and the greenland ice sheet centennial to millennial scale changes in the wider north atlantic region were accompanied by variations in the west greenland current wgc during periods of relatively warm wgc increased surface air temperature over western greenland led to ice sheet retreat and significant meltwater flux in contrast during periods of cold wgc atmospheric cooling resulted in glacier advances we also identify potential linkages between the palaeoceanography of the disko bugt region and key changes in the history of human occupation cooler oceanographic conditions at 3 5 ka bp support the view that the saqqaq culture left disko bugt due to deteriorating climatic conditions the cause of the disappearance of the dorset culture is unclear but the new data presented here indicate that it may be linked to a significant increase in meltwater flux which caused cold and unstable coastal conditions at ca 2 ka bp the subsequent settlement of the norse occurred at the same time as climatic amelioration during the medieval climate anomaly and their disappearance may be related to harsher conditions at the beginning of the little ice age

lithosphere rigidity by adjoint based inversion of interseismic gps data application to the western united states while vertical motion induced by long term geological loads is often used to estimate the flexural rigidity of the lithosphere we intend to evaluate the shear rigidity of the lithosphere using horizontal motion our approach considers that the rigidity of the lithosphere may be defined as its resistance to horizontal tectonic lateral forces in this case a spatial distribution of an effective shear rigidity can be estimated from the analysis of the interseismic velocity fields we consider the western united states zone where weakly strained areas e g the sierra nevada are connected with areas of large strain rate e g san andreas fault system by inverting interseismic strain distribution measured by geodetic methods we infer the effective shear rigidity of the lithosphere the forward problem is defined using the equations of linear elasticity the inversion relies on the minimization of the sum of a quadratic measure of the differences between measured and modelled velocity fields the functional also includes regularization terms for the parameters of the model the gradient of the functional with respect to the minimization parameters is computed using an adjoint formulation this permits the treatment of large dimensional minimization problems finally a measure of the uncertainty of our inversion is illustrated through the covariance matrix of the parameters at the optimum the optimization chart is validated on two synthetic velocity distributions then the effective shear rigidity variations of the western united states are estimated using the cmm3 interseismic velocities the inversion displays low effective rigidities along the san andreas fault system the mojave desert and in the eastern california shear zone while rigid areas are found in the sierra nevada and in the south basin and range finally we discuss the differences between our strain rate and rigidity maps with previously published results for the western united states

long term fault creep observations in central california the u s geological survey usgs has been monitoring aseismic fault slip in central california for more than 10 years as part of an earthquake prediction experiment since 1968 the usgs creep network has grown from one creep meter at the cienega winery south of hollister to a 44 station network that stretches from hayward east of san francisco bay to palmdale in southern california in general the long term slip pattern is most variable on sections of the faults where several magnitude 4 and larger earthquakes occurred during the recording period e g calaveras fault near hollister and san andreas fault between san juan bautista and bear valley these fault sections are the most difficult to characterize with a single long term slip rate in contrast sections of the faults that are seismically relatively quiet e g san andreas fault between bear valley and parkfield produce the steadiest creep records and are easiest to fit with a single long term slip rate appendix is available with entire article on microfiche order from the american geophysical union 2000 florida avenue n w washington d c 20009 document j82 004 1 00 payment must accompany order

first evidences of fast creeping on a long lasting quiescent earthquake normal fault in the mediterranean summary a key issue in our understanding of the earthquake cycle and seismic hazard is the behaviour of an active fault during the interseismic phase locked and creeping faults represent two end members of mechanical behaviours that are given two extreme rupturing hazard levels that is high and low respectively geophysical and space geodetic analyses are carried out over the pollino range an extensional environment within the africa eurasia plate boundary to disclose the behaviour of the long lasting quiescent castrovillari normal fault fault trenching evidenced at least four large earthquakes 6 5 7 0 mw in the past and an elapsed time of 1200 yr since the last event inversion of differential interferometric synthetic aperture radar and global positioning system over a decade shows fast creeping at all depths of the fault plane the velocity strengthening creeping zone reaches maximum rates 20 mm yr 1 against an average rate of about 3 9 mm yr 1 it limits the southern weakening locked part of the fault an essential condition for the generation of a large earthquake on the castrovillari fault as has occurred in the past is a rupture through the velocity strengthening zone the castrovillari fault yields the best evidence for being both a strong and weak fault during its earthquake cycle creeping at rates faster than its tectonically driven ones it must thus consist of a mix of unstable and conditionally stable patches ready to sustain a sizeable earthquake quantifying and mapping the slip rate over the fault plane is important because they influence fault moment budget estimate and helps to constrain constitutive laws of fault zones aseismic slip also redistributes stress in the crust thereby affecting the locations of future earthquakes

accuracy of topographic maps derived from ers 1 interferometric radar an interferometric radar technique for topographic mapping of surfaces promises a high resolution approach to the generation of digital elevation models the authors present analyses of data collected by the synthetic aperture radar instrument on board the ers 1 satellite on successive orbits use of a single satellite in a nearly repeating orbit is attractive for reducing cost and spaceborne hardware complexity also it permits inference of changes in the surface from the correlation properties of the radar echoes the data have been reduced to correlation maps and digital elevation models the correlation maps show that temporal correlation decreases significantly with time but not necessarily at a constant well defined rate likely depending on environmental factors when correlation among passes remains high however it is possible to form digital elevation models analyses of noise expected in ers 1 interferometric data collected over alaska and the southwestern united states indicate that maps with relative errors less than 5 m rms are possible in some regions however orbit uncertainties imply that tie points are required in order to reduce absolute height errors to a similar magnitude the authors find that about 6 tie points per 40 spl times 40 km scene with 5 m rms or better height accuracy are needed to keep systematic map height errors below 5 m rms the performance of the ers 1 radar system for topographic applications though useful for a variety of regional and local discipline studies may be improved with respect to temporal decorrelation errors and absolute height acuity by modifying the orbit repeat period and incorporating precise orbit determination techniques the resulting implementation will meet many but not all objectives of a global mapping mission

mapping small elevation changes over large areas differential radar interferometry a technique that uses synthetic aperture radar sar images to measure very small 1 cm or less surface motions with good resolution 10 m over large swaths 50 km is presented along with experimental results the method could be used for accurate measurements of many geophysical phenomena including swelling and buckling in fault zones residual displacements from seismic events and prevolcanic swelling the method is based on sar interferometry where two images are made of a scene by simultaneously flying two physically separated antennas then the phases of corresponding pixels are differenced and altitude formation is deduced from some simple computation and image rectification it is also possible to use one antenna flown twice over the same scene then if the second flight exactly duplicates the track of the first an interesting possibility occurs there would be no phase changes between the images at all unless there was a physical change in the scene such as ground swelling that would alter the distance from some resolution element to the antenna since the phase changes all occur at the short carrier wavelength the basic limitation on sensitivity is only the phase noise in the system when the two imaging passes are made from flight tracks that are separated which is the case with the seasat images used here it is no longer possible to distinguish surface changes from the parallax caused by topography however with some additional computation a third image made at some other baseline may be used to remove the topography and leave only the surface changes this method was applied using seasat data to an imaging site in imperial valley california where motion effects were observed that were ascribed to the expansion of water absorbing clays phase change images of this area are shown along with associated ground truth about the presence of water problems with the technique are explored along with a discussion of future experimental possibilities on upcoming sar missions like earth observing system eos earth resources satellite ers 1 sir c and the venus imaging radar magellan

aseismic creep along the san andreas fault northwest of parkfield ca measured by radar interferometry ers 1 radar images acquired 14 months apart studied by differential radar interferometry show the wide area distribution of aseismic creep along the fault segment northwest of parkfield california a sharp discontinuity in the interferometric phase of less than 2 cm equivalent line of sight displacement extends over 80 km in the differential interferogram coincident with the mapped trace of the active san andreas fault and consistent with the expected and measured fault motion although patterns of strain associated with the transition from locked to creeping are not clearly identifiable a decrease in creep displacement from northwest to southeast along the fault is visible the observations are in agreement with a model of elastic deformation constrained by in situ data that supports a maximum expected deformation signature of 10 mm across the image

measurement of interseismic strain accumulation across the north anatolian fault by satellite radar interferometry in recent years interseismic crustal velocities and strains have been determined for a number of tectonically active areas through repeated measurements using the global positioning system the terrain in such areas is often remote and difficult and the density of gps measurements relatively sparse in principle satellite radar interferometry can be used to make millimetric precision measurements of surface displacement over large surface areas in practice the small crustal deformation signal is dominated over short time intervals by errors due to atmospheric topographic and orbital effects here we show that these effects can be overcome by stacking multiple interferograms after screening for atmospheric anomalies effectively creating a new interferogram that covers a longer time interval in this way we have isolated a 70 km wide region of crustal deformation across the eastern end of the north anatolian fault turkey the distribution of deformation is consistent with slip of 17 32 mm yr below 5 33 km on the extension of the surface fault at depth if the gps determined slip rate of 24 1 mm yr is accepted the locking depth is constrained to 18 6 km

remote monitoring of the earthquake cycle using satellite radar interferometry the earthquake cycle is poorly understood earthquakes continue to occur on previously unrecognized faults earthquake prediction seems impossible these remain the facts despite nearly 100 years of intensive study since the earthquake cycle was first conceptualized using data acquired from satellites in orbit 800 km above the earth a new technique radar interferometry insar has the potential to solve these problems for the first time detailed maps of the warping of the earth s surface during the earthquake cycle can be obtained with a spatial resolution of a few tens of metres and a precision of a few millimetres insar does not need equipment on the ground or expensive field campaigns so it can gather crucial data on earthquakes and the seismic cycle from some of the remotest areas of the planet in this article i review some of the remarkable observations of the earthquake cycle already made using radar interferometry and speculate on breakthroughs that are tantalizingly close

decorrelation of l band and c band interferometry over vegetated areas in california temporal decorrelation is one of the main limitations for recovering interseismic deformation along the san andreas fault system using interferometric synthetic aperture radar to assess the improved correlation properties of l band with respect to c band we analyzed l band advanced land observation satellite alos interferograms with a range of temporal and spatial baselines over three vegetated areas in california and compared them with corresponding c band european remote sensing satellite ers interferograms over the highly vegetated northern california forests in the coast range area alos remains remarkably well correlated over a 2 year period whereas an ers interferogram with a similar temporal and spatial baseline lost correlation in central california near parkfield we found a similar pattern in decorrelation behavior which enabled the recovery of a fault creep and a local uplifting signal at l band that was not apparent at c band in the imperial valley in southern california both alos and ers have low correlation over farmlands alos has lower correlation over some sandy surfaces than ers probably due to low signal to noise ratio in general l band interferograms with similar seasonal acquisitions have higher correlation than those with dissimilar season for both l and c band correlation over vegetated areas decreases with time for intervals less than 1 year and then remains relatively constant at longer time intervals the decorrelation time for l band is more than 2 years in the forest in california whereas that for c band is less than 6 months overall these results suggest that l band interferograms will reveal near fault interseismic deformation once sufficient data become available

geodetic measurements near parkfield california 1959 1984 trilateration measurements have been made by various agencies since 1959 near parkfield california in the transition zone between the central creeping section and the southern locked section of the san andreas fault within the transition zone there are several creep meters and alignment arrays four small aperture trilateration networks and a broad trilateration network extending 70 km southwest from the san andreas fault to the pacific coast line length changes observed after the 1966 ml 5 6 parkfield earthquake indicate a geodetic moment of 4 5 1 0 1025 dyn cm the data are consistent with either 91 8 cm slip on a rupture zone which is 30 km long and extends from 3 to 8 km below the surface or 59 5 cm on a 30 km long zone 2 10 km deep this moment estimate includes some postseismic slip and is a factor of 2 4 greater than the moment determined from seismic surface waves the post 1966 data set is well suited to discriminate between the effects of surface and deep slip surface slip rates determined by creep meters alinement arrays and small aperture trilateration networks decrease from 29 mm yr at slack canyon to zero south of highway 46 a gradient of roughly 0 48 0 01 mm yr km deformation of a subset of the trilateration network between cholame and san luis obispo is consistent with shallow slip of 2 9 1 2 mm yr from the surface to a depth of 16 km and 33 4 5 5 mm yr below 16 km the trilateration data alone do not uniquely constrain both the transition depth from shallow to deep slip and the deep slip rate a transition depth near 16 km is preferred because it provides the best fit to the data and because the predicted slip rate is consistent with independent estimates of the total slip rate across the san andreas fault this simple two dimensional model neglects along strike variations in the deformation the data show no evidence for significant strike slip deformation across faults between the san andreas and the pacific coast

high resolution interseismic velocity data along the san andreas fault from gps and insar 1 we compared four interseismic velocity models of the san andreas fault based on gps observations the standard deviations of the predicted secular velocity from the four models are larger north of the san francisco bay area near the creeping segment in central california and along the san jacinto fault and the east california shear zone in southern california a coherence spectrum analysis of the secular velocity fields indicates relatively high correlation among the four models at longer wavelengths 15 40 km with lower correlation at shorter wavelengths to improve the short wavelength accuracy of the interseismic velocity model we integrated interferometric synthetic aperture radar insar observations initially from advanced land observing satellite alos ascending data spanning from the middle of 2006 to the end of 2010 totaling more than 1100 interferograms with gps observations using a sum remove filter restore approach the final insar line of sight data match the point gps observations with a mean absolute deviation of 1 5 mm yr we systematically evaluated the fault creep rates along major faults of the san andreas fault and compared them with creepmeters and alignment array data compiled in uniform california earthquake rupture forecast version 2 ucerf2 moreover this insar line of sight dataset can constrain rapid velocity gradients near the faults which are critical for understanding the along strike variations in stress accumulation rate and associated earthquake hazard

precursory analysis of gps time series for seismic hazard assessment we discuss the use of fractal analysis of geophysical big data as a precursory method for the estimation of current seismic hazard we begin by analyzing gps time series of land surface displacements recorded in various regions of the planet exhibiting different degrees of seismic activity we show how the quantitative measure of chaoticity based on a modified detrended fluctuation analysis dfa method can be used to distinguish critical and noncritical regimes of evolution of the earth s crust having established the reference values for the measure of chaoticity we then choose california as the case study region and apply modified dfa to over 1200 time series for determining local areas currently exposed to higher seismic hazard we comprehensively analyze the results obtained and compare them with those produced by conventional risk assessment methods we demonstrate consistency of our results and yet discover that the suggested approach allows us to quantify two qualitatively different mechanisms involved in the growth of seismic hazards we propose a hypothesis which relates these mechanisms to the known mechanisms of earthquake generation that evince a growth of collective behavior in the earth s crust on the eve of an earthquake in order to verify the hypothesis we analyze the same gps data by an independent statistical method canonical coherence analysis cca which permits us to quantify the degree of synchronized behavior of constituents of the earth s crust the cca method confirms our previously obtained estimates thus supporting fractal analysis of gps time series as a suitable precursory method for current seismic hazard assessment

the parkfield california earthquake prediction experiment five moderate magnitude 6 earthquakes with similar features have occurred on the parkfield section of the san andreas fault in central california since 1857 the next moderate parkfield earthquake is expected to occur before 1993 the parkfield prediction experiment is designed to monitor the details of the final stages of the earthquake preparation process observations and reports of seismicity and aseismic slip associated with the last moderate parkfield earthquake in 1966 constitute much of the basis of the design of the experiment