the role of kelp in sediment transport observations from southeast new zealand abstract large marine algae such as kelp can when dislodged remove part of the substrate to which they are attached and subsequently transport it quantification of this process and the causes behind it have rarely been investigated this study examines sediment transport by the kelps durvillaea antarctica and durvillaea willana in southeast new zealand five beaches near dunedin were surveyed weekly for 30 weeks and all beach cast kelp was counted and identified the weight and nature of any attached sediment was also recorded additionally 60 sections of the southeast new zealand coastline totaling 130 km were surveyed once and all beach cast kelp examined rocks were found to be attached to 27 of examined holdfasts usually occurring as a thin veneer the weight per holdfast ranged from 0 1 g to 83 kg with an unusual outlier of 365 kg with a mean weight of 77 1 g se 15 3 n 1560 most holdfasts transported less than 100 g carbonate material occurred on 84 of holdfasts with weights per holdfast ranging from 0 02 to 116 56 g with a mean of 7 8 g se 0 3 n 1695 the character of local rock strongly influences the kelp mediated flux south coast beaches with schist rocks nearby received a significantly greater mean flux 7 49 g m2 year 1 than basalt surrounded peninsula beaches mean flux 0 50 g m2 year 1 kelp transported material provides a small but significant source of sediment to beaches in southeast new zealand and therefore should be considered when constructing sediment budgets in coastal areas this study has shown that it is often necessary for geologists to consider biological processes

the algal lift buoyancy mediated sediment transport the role of benthic algae as biostabilizers of sediments is well known however their potential to lift and transport sediments remains unclear under low flow conditions matured algal mats may detach from the bed and may lift up sediment thereby causing disturbance to the uppermost streambed sediment we tested the potential of algal mats to lift sediments in 12 indoor flumes filled with sand 0 2 0 8 mm gravel 2 8 mm or a sand gravel mixture 25 75 mass after four weeks the algal mats covered about 50 of the flumes area due to the accumulation of oxygen gas bubbles in the mats that developed from high primary production at 4 5 weeks about half of the algal mats detached from the bed carrying entangled sediments both the area covered by algal mats and detached area were similar among sediment types but the amount of sediment transported tended to be higher for sand and sand gravel mixture compared to gravel our results reveal that biologically mediated sediment transport mainly depends on the development of a dense filamentous algal matrix that traps gas bubbles increasing the mats buoyancy this novel mechanism of sediment transport will occur in shallow ecosystems during low flow periods with the highest impact for sandy sediments

triggered surface slips in the salton trough associated with the 1999 hector mine california earthquake surface fracturing occurred along the southern san andreas superstition hills and imperial faults in association with the 16 october 1999 mw 7 1 hector mine earthquake making this at least the eighth time in the past 31 years that a regional earthquake has triggered slip along faults in the salton trough fractures associated with the event formed discontinuous breaks over a 39 km long stretch of the san andreas fault from the mecca hills southeastward to salt creek and durmid hill a distance from the epicenter of 107 to 139 km sense of slip was right lateral only locally was there a minor 1 mm vertical component of slip dextral slip ranged from 1 to 13 mm maximum slip values in 1999 and earlier triggered slips are most common in the central mecca hills field evidence indicates a transient opening as the hector mine seismic waves passed the southern san andreas fault comparison of nearby strong motion records indicates several periods of relative opening with passage of the hector mine seismic wave a similar process may have contributed to the field evidence of a transient opening slip on the superstition hills fault extended at least 9 km at a distance from the hector mine epicenter of about 188 to 196 km this length of slip is a minimum value because we saw fresh surface breakage extending farther northwest than our measurement sites sense of slip was right lateral locally there was a minor 1 mm vertical component of slip dextral slip ranged from 1 to 18 mm with the largest amounts found distributed or skewed away from the hector mine earthquake source slip triggered on the superstition hills fault commonly is skewed away from the earthquake source most notably in 1968 1979 and 1999 surface slip on the imperial fault and within the imperial valley extended about 22 km representing a distance from the hector mine epicenter of about 204 to 226 km sense of slip dominantly was right lateral the right lateral component of slip ranged from 1 to 19 mm locally there was a minor 1 2 mm vertical component of slip larger proportions of vertical slip up to 10 mm occurred in mesquite basin where scarps indicate long term oblique slip motion for this part of the imperial fault slip triggered on the imperial fault appears randomly distributed relative to location along the fault and source direction multiple surface slips both primary and triggered slip indicate that slip repeatedly is small at locations of structural complexity

triggered slip along the san andreas fault after the 8 july 1986 north palm springs earthquake in addition to minor surface cracks in the region of the 8 july 1986 north palm springs earthquake minor aseismic surficial rupture occurred along three segments of the san andreas fault 44 to 86 km southeast of the epicenter data from a creepmeter and a tiltmeter at one locality suggest that triggered slip occurred coseismically beneath the instruments but took 33 hr to propagate to the surface that slippage occurred coseismically at depth favors mechanisms for triggered slip that involve dynamic or static strain changes rather than creep migrating from the source region the distribution of slip along the san andreas fault associated with the north palm springs earthquake differed significantly from that recorded after the moderate 1968 borrego mountain california and 1979 imperial valley california earthquakes during these earthquakes triggered slip occurred along the san andreas fault in the durmid hill area and in the mecca hills triggered slip associated with the north palm springs earthquake occurred in these two areas again but also extended farther northwest into the indio hills where as much as 9 mm of dextral slip occurred in the mecca hills surface cracks in 1986 appeared over a shorter fault length than in previous events and the dextral displacement was smaller with maximum values of only 2 to 3 mm on durmid hill surface cracks in 1986 were localized along a 200 m long stretch of the fault spanning the mecca beach creepmeter and extending about 150 m to the southeast right lateral displacements on surface cracks in this area were 1 4 to 2 0 mm smaller than those observed in previous events although the mechanism of triggered aseismic slip is poorly understood examination of displacement rates for the past several decades to centuries may indicate whether the aseismic slip rate is constant or represents accelerating premonitory failiure of the southernmost san andreas fault

investigation of nearfield postseismic slip following the mw 7 3 landers earthquake sequence of 28 june 1992 california repeated precise surveys of six nearfield trilateration arrays reveal that minor horizontal displacements occurred across the several fault ruptures in the five months following the landers earthquake sequence the displacements range from 0 2 mm on the camp rock and emerson faults to 3 2 mm on the landers fault to 9plusmn 2 mm on the johnson valley fault to 40 5 mm on the eureka peak fault consistent in magnitude and duration with gps and creepmeter measurements by other investigators the relative lack of afterslip at all sites except across the eureka peak fault is probably due to the lack of a thick alluvial cover concomitant precise resurveys of level lines across the san andreas fault in coachella valley and of a trilateration array at durmid hill south easternmost san andreas fault failed to reveal vertical or horizontal displacements greater than the allowable uncertainty 1 mm for leveling 2 mm 2 ppm for trilateration therefore the landers earthquake sequence did not perturb the san andreas in any way that was evident from our measurements of near surface strain

voyages of seaweeds the role of macroalgae in sediment transport abstract at least 26 genera of macroalgae have been observed attached to and carrying sedimentary materials rock veneer or carbonate to beaches and the sea floor most studies have been descriptive with few quantifying flux rates this study reviews and quantifies the mainly biological literature on macroalgae mediated sediment transport in coastal and marine environments dislodgement of macroalgae from a hard substrate can result in erosion up to 0 01 mm y 1 the proportion of buoyant macroalgae carrying rock material usually a thin veneer but sometimes boulders up to 365 kg varies by location but can reach as high as 35 macroalgae carrying attached carbonate material e g crustose coralline algae shells are more common up to 85 of holdfasts on a beach may contain up to 116 g caco 3 each sand and carbonate trapped in haptera along with encrusting carbonate producing organisms have a mass of up to tens of grammes while most dislodged macroalgae land close to where they came from others may be stranded many thousands of km from their place of origin sediment deposited by macroalgal transport depends largely on the characteristics of local source rocks while hard rocks may only provide a few g m 2 y 1 highly fractured basalt has been shown to provide up to 78 g m 2 y 1 rock transport by macroalgae is less than carbonate flux which may reach over 8000 g m 2 y 1 based on the projected abundance of macroalgal rafts some 350 tonnes of sediment both carbonate and clastic may be afloat in the southern ocean at any one time macroalgal transport may explain the presence of exotic rocks and shells found far from their source environment while cold climate rafting of sediment is dominated by glacial processes in warm periods rafting may be limited to biological transport overall the transport of rock and carbonate by macroalgae has the potential in some environments of being a significant source of sediment

behavior of the southernmost san andreas fault during the past 300 years surficial creep occurs at low rates along the coachella valley segment of the san andreas fault which has not produced a large earthquake during the period of historical record geodetic data indicate however that the crust adjacent to this segment of the san andreas fault is accumulating strain at a high rate furthermore neotectonic and paleoseismic data indicate that the fault does produce very large earthquakes every two to three centuries in view of its long term behavior the occurrence of creep along the surficial trace of the fault in the coachella valley is of particular interest along two short reaches of the san andreas fault in the coachella valley measurements of offset geological deposits and man made structures and from alignment arrays and creep meters show that slip rates of 2 4 mm yr near indio and near the salton sea have persisted for the past three centuries this slow aseismic surficial creep is not a transient precursor to seismic failure of this segment of the fault we suggest that the coachella valley segment of the san andreas fault creeps in its upper few kilometers this behavior may be due to tectonically induced high pore pressures in the coarse sediments that abut the fault

interseismic strain localization in the san jacinto fault zone we investigate interseismic deformation across the san jacinto fault at anza california where previous geodetic observations have indicated an anomalously high shear strain rate we present an updated set of secular velocities from gps and insar observations that reveal a 2 3 km wide shear zone deforming at a rate that exceeds the background strain rate by more than a factor of two gps occupations of an alignment array installed in 1990 across the fault trace at anza allow us to rule out shallow creep as a possible contributor to the observed strain rate using a dislocation model in a heterogeneous elastic half space we show that a reduction in shear modulus within the fault zone by a factor of 1 2 1 6 as imaged tomographically by allam and ben zion geophys j int 190 1181 1196 2012 can explain about 50 of the observed anomalous strain rate however the best fitting locking depth in this case 10 4 1 3 km is significantly less than the local depth extent of seismicity 14 18 km we show that a deep fault zone with a shear modulus reduction of at least a factor of 2 4 would be required to explain fully the geodetic strain rate assuming the locking depth is 15 km two alternative possibilities include fault creep at a substantial fraction of the long term slip rate within the region of deep microseismicity or a reduced yield strength within the upper fault zone leading to distributed plastic failure during the interseismic period

triggered slip on the calaveras fault during the magnitude 7 1 loma prieta california earthquake after the magnitude m 7 1 loma prieta earthquake on the san andreas fault the authors inspected selected sites along the calaveras fault for evidence of recent surface displacement in two areas along the calaveras fault they documented recent right lateral offsets of cultural features by at least 5 mm within zones of recognized historical creep the areas are in the city of hollister and at highway 152 near san felipe lake located approximately 25 km southeast and 18 km northeast respectively of the nearest part of the san andreas rupture zone on the basis of geologic evidence the times of the displacement events are constrained to within days or hours of the loma prieta mainshock they conclude that this earthquake on the san andreas fault triggered surface rupture along at least a 17 km long segment of the calaveras fault these geologic observations extend evidence of triggered slip from instrument stations within this zone of calaveras fault rupture

carbonate sediment production by sargassum epibionts abstract sargassum and associated calcareous epibionts were collected at sea and on a bermuda beach the weight percent of calcium carbonate produced by epibionts averaged 9 4 for samples collected at sea and 5 3 for beached samples this indicates that sargassum epibionts are a major potential source of carbonate sediment beached sargassum adds between 8 213 g m2 yr and 3 431 g m2 yr to the sampled beach and is a significant actual source of carbonate sediment

pre earthquake displacement and triggered displacement on the imperial fault associated with the superstition hills earthquake of 24 november 1987 two right lateral slip events about 3 weeks apart in november 1987 broke the surface discontinuously along probably similar nearly 20 km lengths of the northern imperial fault the first displacement at about the beginning of november was accompanied by a surface tilt representing deep vertical motion or distributed strain this movement may have been part of a more regional event that also involved the southern san andreas fault although the evidence there is questionable the later surface offset was triggered probably by the second main shock of the 24 november earthquakes located in the superstition hills about 37 km northwest of the imperial fault the maximum observed displacement was less than 4 cm on both occasions for the triggered movement the maximum slip occurred on a branch strand near the northern extremity of the fault pre earthquake resurveys of short length leveling lines indicated combined surface displacement and an eastward tilt at two locations between surveys 7 1 2 months apart and 13 months apart the tilt at harris road during this pre earthquake interval is modeled as a 1 4 cm vertical component of slip deeper than 100 m on a 70 northeastward dipping fault later resurveys showed a marked reduction of deep movement in the time period including the triggered slip and between december 1987 and january 1988 it had ceased no definite evidence of surface fracturing was found in the brawley fault zone during either period of time when the imperial fault moved remeasurement of leveling lines there indicated small very near surface vertical components of movement in the northern half of the zone elevation changes in the southern part indicated distributed strain and or movement only deeper than about 50 m the brawley zone changes are not fixed in time well enough to clearly relate them to the surface movements on the imperial fault

coseismic fault slip associated with the 1992 m w 6 1 joshua tree california earthquake implications for the joshua tree landers earthquake sequence coseismic surface deformation associated with the mw 6 1 april 23 1992 joshua tree earthquake is well represented by estimates of geodetic monument displacements at 20 locations independently derived from global positioning system and trilateration measurements the rms signal to noise ratio for these inferred displacements is 1 8 with near fault displacement estimates exceeding 40 mm in order to determine the long wavelength distribution of slip over the plane of rupture a tikhonov regularization operator is applied to these estimates which minimizes stress variability subject to purely right lateral slip and zero surface slip constraints the resulting slip distribution yields a geodetic moment estimate of 1 7 1018 n m with corresponding maximum slip around 0 8 m and compares well with independent and complementary information including seismic moment and source time function estimates and main shock and aftershock locations from empirical green s function analyses a rupture duration of 5 s is obtained which implies a rupture radius of 6 8 km most of the inferred slip lies to the north of the hypocenter consistent with northward rupture propagation stress drop estimates are in the range of 2 4 mpa in addition predicted coulomb stress increases correlate remarkably well with the distribution of aftershock hypocenters most of the aftershocks occur in areas for which the mainshock rupture produced stress increases larger than about 0 1 mpa in contrast predicted stress changes are near zero at the hypocenter of the mw 7 3 june 28 1992 landers earthquake which nucleated about 20 km beyond the northernmost edge of the joshua tree rupture based on aftershock migrations and the predicted static stress field we speculate that redistribution of joshua tree induced stress perturbations played a role in the spatio temporal development of the earthquake sequence culminating in the landers event

surface displacement on the imperial and superstition hills faults triggered by the westmorland california earthquake of 26 april 1981 parts of the imperial and the superstition hills faults moved right laterally at the ground surface at the time of or shortly following the ml 5 6 westmorland earthquake of 26 april 1981 the displacements probably occurred before any significant aftershocks on either fault and thus are classed as triggered slips although the main shock was located in an exceptionally seismogenic part of imperial valley about 20 km distant from either fault no clear evidence of past surface faulting is known in the epicentral area horizontal displacement on the imperial and superstition hills faults southeast and southwest of the epicenter respectively reached maxima of 8 and 14 mm and the discontinuous surface ruptures formed along approximately equal lengths of northern segments of the two structures 16 8 and 15 7 km respectively the maximum vertical component of slip measured on surface cracks on the imperial fault 6 mm was located on the west side of mesquite basin near harris road leveling data at harris road suggest slightly larger vertical movement at the surface there fault dislocation modeling of this leveling data further suggests that the maximum shallow subsurface dip slip component of the triggered movement was as much a factor of 4 larger than that measured at the fault trace the map pattern of the rupture may reveal the principal strand among the several near the north end of the imperial fault no surface displacement was found along traces of the brawley fault zone the san andreas fault or the part of the coyote creek fault that slipped during the 1968 borrego mountain earthquake ground search in the epicentral area of the main shock and in the widely dispersed aftershock region in northern imperial valley failed to locate any definite evidence of new surface faulting

the emerson lake body a link between the landers and hector mine earthquakes southern california as inferred from gravity and magnetic anomalies gravity and magnetic data indicate a mafic crustal heterogeneity that lies between the hector mine 16 october 1999 m w 7 1 and landers 28 june 1992 m w 7 3 epicenters the aftershocks and ruptures of these two events avoided the interior of the body two and three dimensional modeling of the potential field anomalies shows that the source here named the emerson lake body elb extends to a depth of approximately 15 km the source of the gravity and magnetic anomaly is most likely jurassic diorite because exposures of these rocks coincide with both gravity and magnetic highs west of emerson lake seismic tomography also shows higher velocities within the region of the elb we propose that the elb was an important influence on the rupture geometry of the landers and hector mine ruptures and that the elb may have played a role in transferring of stress from the landers earthquake to the hector mine hypocenter seismicity before the landers earthquake also tended to avoid the elb suggesting that the elb affects how strain is distributed in this part of the mojave desert thus faults within the body should have limited rupture sizes and lower seismic hazard than faults bounding or outside this mafic crustal heterogeneity

changes in static stress on southern california faults after the 1992 landers earthquake the magnitude 7 5 landers earthquake of 28 june 1992 was the largest earthquake to strike california in 40 years the slip that occurs in such an earthquake would be expected to induce large changes in the static stress on neighbouring faults these changes in stress should in turn affect the likelihood of future earthquakes stress changes that load faults towards failure have been cited as the cause of small1 5 moderate6 and large7 earthquakes conversely those that relax neighbouring faults have been related to a decrease in seismicity5 here we use an elastic half space model8 to estimate the stress changes produced by the landers earthquake on selected southern california faults including the san andreas we find that the estimated stress changes are consistent with the triggering of four out of the five aftershocks with magnitude greater than 4 5 and that the largest changes 1 10 bar occurring on part of the san bernardino segment of the san andreas fault may have decreased the time to the next magnitude 8 earthquake by about 14 years

surface deformation associated with fractures near the 2019 ridgecrest earthquake sequence contemporary earthquake hazard models hinge on an understanding of how strain is distributed in the crust and the ability to precisely detect millimeter scale deformation over broad regions of active faulting satellite radar observations revealed hundreds of previously unmapped linear strain concentrations or fractures surrounding the 2019 ridgecrest earthquake sequence we documented and analyzed displacements and widths of 169 of these fractures although most fractures are displaced in the direction of the prevailing tectonic stress prograde a large number of them are displaced in the opposite retrograde direction we developed a model to explain the existence and behavior of these displacements a major implication is that much of the prograde tectonic strain is accommodated by frictional slip on many preexisting faults

triggered surface slips in the coachella valley area associated with the 1992 joshua tree and landers california earthquakes the coachella valley area was strongly shaken by the 1992 joshua tree 23 april and landers 28 june earthquakes and both events caused triggered slip on active faults within the area triggered slip associated with the joshua tree earth quake was on a newly recognized fault the east wide canyon fault near the south western edge of the little san bernardino mountains slip associated with the land ers earthquake formed along the san andreas fault in the southeastern coachella valley surface fractures formed along the east wide canyon fault in association with the joshua tree earthquake the fractures extended discontinuously over a 1 5 km stretch of the fault near its southern end sense of slip was consistently right oblique west side down similar to the long term style of faulting measured offset values were small with right lateral and vertical components of slip ranging from 1 to 6 mm and 1 to 4 mm respectively this is the first documented historic slip on the east wide canyon fault which was first mapped only months before the joshua tree earthquake surface slip associated with the joshua tree earthquake most likely de veloped as triggered slip given its 5 km distance from the joshua tree epicenter and aftershocks as revealed in a trench investigation slip formed in an area with only a thin 3 m thick veneer of alluvium in contrast to earlier documented triggered slip events in this region all in the deep basins of the salton trough a paleoseismic trench study in an area of 1992 surface slip revealed evidence of two and possibly three surface faulting events on the east wide canyon fault during the late quaternary probably latest pleistocene first event and mid to late holocene second two events about two months after the joshua tree earthquake the landers earthquake then triggered slip on many faults including the san andreas fault in the southeastern coachella valley surface fractures associated with this event formed discontinuous breaks over a 54 km long stretch of the fault from the indio hills southeastward to durmid hill sense of slip was right lateral only locally was there a minor 1 mm vertical component of slip measured dextral displacement values ranged from 1 to 20 mm with the largest amounts found in the mecca hills where large slip values have been measured following past triggered slip events

the movement of gravel by the alga fucus vesiculosus l on an arctic intertidal flat abstract measurements of the weights of gravel clasts with attached fucoid algae fucus vesiculosus from an arctic intertidal flat at pangnirtung in northern canada indicate that stones are floated when the algae is at least three times heavier than the clast when the algae is not large enough to float the clast to which it is attached the form drag and lift which it provides allow moderate tidal currents to move very much larger stones than would be possible otherwise these mechanisms offer a means of transporting coarse sediments to deep water where they may augment or be confused with ice rafted materials

uncertainties in slip rate estimates for the mission creek strand of the southern san andreas fault at biskra palms oasis southern california this study focuses on uncertainties in estimates of the geologic slip rate along the mission creek strand of the southern san andreas fault where it offsets an alluvial fan t2 at biskra palms oasis in southern california we provide new estimates of the amount of fault offset of the t2 fan based on trench excavations and new cosmogenic 10be age determinations from the tops of 12 boulders on the fan surface we present three alternative fan offset models a minimum a maximum and a preferred offset of 660 m 980 m and 770 m respectively we assign an age of between 45 and 54 ka to the t2 fan from the 10be data which is significantly older than previously reported but is consistent with both the degree of soil development associated with this surface and with ages from u series geochronology on pedogenic carbonate from t2 described in a companion paper by fletcher et al this volume these new constraints suggest a range of slip rates between 12 and 22 mm yr with a preferred estimate of 14 17 mm yr for the mission creek strand of the southern san andreas fault previous studies suggested that the geologic and geodetic slip rate estimates at biskra palms differed we find however that considerable uncertainty affects both the geologic and geodetic slip rate estimates such that if a real discrepancy between these rates exists for the southern san andreas fault at biskra palms it cannot be demonstrated with available data

southern surface rupture associated with the 1992 m7 4 landers earthquake did it all happen during the mainshock approximately three minutes after the magnitude 7 4 landers mainshock on 28 june 1992 a m5 7 aftershock occurred south of the mainshock epicenter with a location of 34 7 65 n 116 23 82 w this aftershock was recorded on an array of portable digital seismic instruments deployed in morongo valley 21 km southwest of the event although peak accelerations are found to differ by approximately 50 at stations with similar general site conditions within 500 m of each other there is good coherence of arrivals across the array for frequencies 1 hz we use the recordings to determine the apparent phase velocity and azimuth of propagation across the array and show that the event clearly ruptured to the south with a rupture length of 11 km and a rupture velocity of approximately 3 0 km s our results suggest that at least some of the mapped surface rupture south of the town of yucca valley 11 km in extent maximum displacement of 20 cm may have been associated with this aftershock if this is the case then the fault that produced the southern end of the landers mainshock the johnson valley fault need not continue at depth across the active left lateral east west trending pinto mountain fault

multiple precursors to the landers earthquake we present evidence for several temporally related premonitory movements preceding the landers earthquake of 28 june 1992 premonitory movements were measured at alignment arrays spanning the northeast painted canyon and san andreas faults in mecca hills california a transitory fault normal extension of 30 3 mm to eight targets was measured twice on 8 and 9 march 1992 and 7 and 8 june 1992 across the northeast and painted canyon faults at the hidden spring wash site hsws four kilometers northwest of the hsws simultaneous fault normal extensions of 24 21 and 6 6 mm were measured across a previously locked 12 km segment of the san andreas fault on 6 june 1992 22 days prior to the landers earthquake a linear regression fit of horizontal displacement at hsws showed a distinct increase in horizontal angles for those targets spanning active faults on the same dates as the fault normal extension for the first time other than a few small events on the north shore creepmeter dextral slip was measured on a nontranspressive parallel slip segment of the san andreas on 6 june 1992 we measured offsets of 14 8 and 3 arc sec 3 sec at the indian stone ring site isrs on the san andreas fault which translates into movement of 20 18 and 9 mm triggered slip was not observed on the main trace of the san andreas fault after the joshua tree earthquake but 17 mm of dextral slip possibly coseismic with the landers earthquake was measured along cracks on 5 july 1992 this amount of slip supports the magnitude of premonitory movement taken together substantial simultaneous fault normal extension and lateral slip at three alignment arrays across three faults followed by a large triggered slip event provide strong evidence for the occurrence of precursors to the landers earthquake

insar imaging of displacement on flexural slip faults triggered by the 2013 mw 6 6 lake grassmere earthquake central new zealand interferometric synthetic aperture radar insar data reveal surface slip on multiple faults triggered by the 2013 mw 6 6 lake grassmere earthquake new zealand surface offsets of 1 2 cm occurred on previously inferred flexural slip faults located 4 km from the epicenter we document dip slip on at least three different northeast striking northwest dipping flexural slip faults located in the western limb of a syncline the along strike extent of the triggered slip is 1 1 5 km for each fault dislocation models suggest that triggered slip is confined to shallow depths 800 m coulomb stress analysis indicates that slip was not triggered by the static stress change of the main shock but was likely caused by dynamic shaking during the passage of seismic waves our finding also provides an important clue on how some slip on shallow flexural slip faults takes place

effect of the loma prieta earthquake on surface slip along the calaveras fault in the hollister area over the past ten years the author has made over 800 measurements of slip rates at 20 sites on various faults in the san francisco bay region this data set enables them to compare rates and amounts of slip on these various faults before and after the loma prieta earthquake lpeq on the san andreas fault no surface slip rate changes associated with the earthquake occurred at any of the sites on the san andreas hayward northern calaveras concord green valley seal cove san gregorio antioch rodgers creek or west napa faults the lpeq apparently triggered up to 12 14 mm of right slip on the southern calaveras fault at two sites in the hollister area less than 50 km from the epicenter most of this slip was probably coseismic or nearly so about the same amount of slip was triggered at these sites in 1984 by the morgan hill earthquake this slip in contrast occurred as afterslip within about a 2 5 month interval the calaveras fault in the hollister area moves episodically with shorter times of more rapid slip alternating with longer times of slower slip the alternation occurs whether or not the times of faster slip are triggered by any nearby seismicmore event s less

erratic continental rocks on volcanic seamounts off the us west coast sampling of volcanic seamounts with dredges and the remotely operated vehicle tiburon recovered erratic rocks in surprising abundance as far as 500km offshore of the us west coast the erratics usually have continental lithologies and appear to have been weathered in nearshore environments they are probably transported by kelp holdfasts drift logs and pinnipeds to the seamounts where they accumulate over time the erratics are concentrated as lag deposits and kept from becoming buried in sediment by currents that sweep the seamounts the erratics often have thinner manganese oxide crusts than rocks of the seamounts because they were delivered to the seafloor more recently and manganese oxide crusts precipitate over time the thinner crusts make erratics easier to collect while most of the erratics clearly did not originate by the volcanic processes that formed the seamounts careful evaluation of some is necessary to distinguish them as erratics failure to recognize the presence of erratics may result in unrealistically complex interpretations of regional geology

new evidence on the slip rate renewal time and late holocene surface displacement southernmost san andreas fault mecca hills california we estimate a renewal time for large earthquakes on the southernmost san andreas fault saf of 260 100 years based on new paleoseismological data and a 34 millennia slip rate of 5 8 mm yr our mean recurrence interval 260 100 is longer and its variance is smaller than the 160 240 93 estimate for a m 7 earthquake used by the working group on california earthquake probabilities wgcep 1995 a smaller creep rate than on contiguous 12 km fault segments is explained by global positioning system data that reveals 2 4 mm yr of creep on the recently discovered witbaard fault that bypasses the 12 km long north shore strand of the saf geomorphic features near an archaeological site that cross the fault allow us to measure displacements of 155 25 cm based on right lateral gully offsets by the most recent earthquake e g 1690 an indian stone ring straddling the fault trace is currently offset 142 12 cm the ring lies on the 12 km long north shore segment of the saf that has accumulated a minimum of 30 mm of triggered slip and aseismic creep since 1969 contrasting slip rates of 23 35 mm yr near indio and 5 14 mm yr on the southernmost saf suggest that the coachella valley strand may be comprised of two distinct segments smaller long term strain accumulation along the southernmost segment probably reduces earthquake potential for that area

rafting rocks reveal marine biological dispersal a case study using clasts from beach cast macroalgal holdfasts abstract tracking and quantifying biological dispersal presents a major challenge in marine systems most existing methods for measuring dispersal are limited by poor resolution and or high cost here we use geological data to quantify the frequency of long distance dispersal in detached bull kelp phaeophyceae durvillaea in southern new zealand geological resolution in this region is enhanced by the presence of a number of distinct and readily identifiable geological terranes we sampled 13 815 beach cast bull kelp plants across 130 km of coastline rocks were found attached to 2639 of the rafted plants and were assigned to specific geological terranes source regions to quantify dispersal frequencies and distances although the majority of kelp associated rock specimens were found to be locally derived a substantial number 4 showed clear geological evidence of long distance dispersal several having travelled over 200 km from their original source regions the proportion of local versus foreign clasts varied considerably between regions while short range dispersal clearly predominates long distance travel of detached bull kelp plants is shown to be a common and ongoing process that has potential to connect isolated coastal populations geological analyses represent a cost effective and powerful method for assigning large numbers of drifted macroalgae to their original source regions

the role of attached kelp seaweed in lowering threshold of coarse gravel entrainment in tidal flows lag deposits of cobble sized clasts found within the troughs of fine gravel dunes on a rock bed intertidal zone are explained by the process of enhanced fluid transport due to attached seaweed field determinations of the competence of the tidal currents demonstrated that the currents were not able to transport weed free clasts on the tidal flat controlled flume experiments were used to demonstrate that the presence of the fucoid alga fucus vesiculosus l attached to clasts reduces the critical velocities and shear stresses to levels that allow the tidal currents to entrain the clasts and move them over the backs of dunes to the lee sides subsequent burial of the weedy clasts in the dune troughs by dune progression kills the weed leaving the latterly exposed clasts as an accumulating weed free lag the weight of attached weed typically equals the submerged weight of the clast and the critical velocity and critical shear stress for initial motion are both roughly halved by the presence of the weed the drag induced by weed is four times that experienced by weed free clasts and mobile clasts exhibit near equal mobility

seaweed assisted benthic gravel transport by tidal currents abstract traction transport of pebbles and cobbles occurs subtidally at current velocities below 0 5 m s 1 when seaweed attached to clasts provides additional lift and drag to the clast in the juan de fuca strait british columbia canada the seaweed cymanthere triplicata commonly attaches to pebbles and provides sufficient additional surface area for tidal currents to drag the clast along the seafloor using in situ measurements of current velocities at 13 m water depth the threshold for initiation of motion of a 30 mm pebble with attached seaweed is 0 3 m s 1 this is approximately one order of magnitude less than the activation velocity for a 30 mm pebble without attached seaweed in addition to kelp rafted floated gravel seaweed assisted benthic gravel transport is possible in marine settings where unidirectional currents e g tidal currents storm induced bottom currents are sufficient to transport pebbles alongshore and into and across the offshore below fairweather wave base if preserved in the rock record deposits of algal enhanced gravel deposited via unidirectional subtidal currents will likely appear as isolated gravel clasts encased in sandstone reflecting the similar current velocities required to transport these two clast groups

fault slip in southern california measurements of slip on major faults in southern california have been performed over the past 18 yr using principally theodolite alignment arrays and tautwire extensometers they provide geodetic control within a few hundred meters of the fault traces which complements measurements made by other techniques at larger distances approximately constant slip rates of from 0 5 to 5 mm yr over periods of several years have been found for the southwestern portion of the garlock fault the banning and san andreas faults in the coachella valley the coyote creek fault the superstition hills fault and an unnamed fault 20 km west of el centro these slip rates are typically an order of magnitude below displacement rates that have been geodetically measured between points at greater distances from the fault traces exponentially decaying postseismic slip in the horizontal and vertical directions due to the 1979 imperial valley earthquake has been measured it is similar in magnitude to the coseismic displacements analysis of seismic activity adjacent to slipping faults has shown that accumulated seismic moment is insufficient to explain either the constant or the decaying postseismic slip thus the mechanism of motion may differ from that of slipping faults in central california which move at rates close to the plate motion and are accompanied by sufficient seismic moment seismic activity removed from the slipping faults in southern california may be driving their relatively aseismic motion

seismic behavior of the southern san andreas fault zone in the northern coachella valley california comparison of the 1948 and 1986 earthquake sequences moderate earthquakes in 1948 and 1986 that occurred along the southern san andreas fault zone are examined to help understand the subsurface geometry and seismic behavior of active fault segments in the northern coachella valley the 1986 north palm springs earthquake occurred between the banning and mission creek traces of the san andreas fault zone based on data from both portable and permanent stations aftershocks of the 1986 event define a nearly planar surface that strikes about n60 to 70 w is about 15 km long and dips northeast from near the banning surface trace at about 45 to 50 relocation of the mainshock using revised station corrections and a local velocity model inverted from the aftershock arrival times indicates a location at 34 n00 26 116 w36 34 and a focal depth of 10 4 km the first motion focal mechanism for the mainshock indicates pure right slip on a plane dipping northeast at 40 to 45 with a strike of n60 w previous moment tensor solutions e g hartzell 1989 exhibit significant oblique reverse slip on a plane with a more westerly strike and a seismic moment of 1 4 to 1 7 1018 n m mw 6 1 actual and synthetic wood anderson recordings indicate a local magnitude of ml 6 0 the 1948 desert hot springs earthquake produced waveforms similar to 1986 although amplitudes for 1948 are typically 20 to 30 larger the 1948 mainshock is relocated at 33 n55 2 116 w28 9 with a focal depth of 12 km a revised magnitude of ml 6 3 and an estimated seismic moment of 2 to 3 1018 n m based on arrival time information from close 20 km portable stations deployed in 1948 to 1949 the 1948 aftershock distribution is about 15 km long 8 to 10 km wide and abuts the 1986 aftershock sequence to the southeast along the banning fault the 1948 aftershock zone is consistent with a focal mechanism that exhibits predominantly right slip motion rake 169 on a plane that strikes n55 w and dips more steeply northeast at 60 to 70 in 1986 the horizontal extent of the rupture may have been controlled by secondary cross faults and possible changes in fault geometry while the down dip extent may have been controlled by the presence at depth of a regional detachment in 1948 the rupture likely had a steeper dip than in 1986 and extended southeast as far as the northern indio hills where the surface trace of the banning fault undergoes an approximate 7 change in strike these results indicate that the banning fault is nonvertical is likely segmented according to fault dip as well as fault strike and has been the primary locus of recent moderate sized earthquake activity in the northern coachella valley

timing of large earthquakes since a d 800 on the mission creek strand of the san andreas fault zone at thousand palms oasis near palm springs california paleoseismic investigations across the mission creek strand of the san andreas fault at thousand palms oasis indicate that four and probably five surface rupturing earthquakes occurred during the past 1200 years calendar age estimates for these earthquakes are based on a chronological model that incorporates radiocarbon dates from 18 in situ burn layers and stratigraphic ordering constraints these five earthquakes occurred in about a d 825 770 890 mean 95 range a d 982 840 1150 a d 1231 1170 1290 a d 1502 1450 1555 and after a date in the range of a d 1520 1680 the most recent surface rupturing earthquake at thousand palms is likely the same as the a d 1676 35 event at indio reported by sieh and williams 1990 each of the past five earthquakes recorded on the san andreas fault in the coachella valley strongly overlaps in time with an event at the wrightwood paleoseismic site about 120 km northwest of thousand palms oasis correlation of events between these two sites suggests that at least the southernmost 200 km of the san andreas fault zone may have ruptured in each earthquake the average repeat time for surface rupturing earthquakes on the san andreas fault in the coachella valley is 215 25 years whereas the elapsed time since the most recent event is 326 35 years this suggests the southernmost san andreas fault zone likely is very near failure the thousand palms oasis site is underlain by a series of six channels cut and filled since about a d 800 that cross the fault at high angles a channel margin about 900 years old is offset right laterally 2 0 0 5 m indicating a slip rate of 4 2 mm yr this slip rate is low relative to geodetic and other geologic slip rate estimates 26 2 mm yr and about 23 35 mm yr respectively on the southernmost san andreas fault zone possibly because 1 the site is located in a small step over in the fault trace and so the rate is not be representative of the mission creek fault 2 slip is partitioned northward from the san andreas fault and into the eastern california shear zone and or 3 slip is partitioned onto the banning strand of the san andreas fault zone

state of stress from focal mechanisms before and after the 1992 landers earthquake sequence the state of stress in the eastern california shear zone ecsz changed significantly because of the occurrence of the 1992 m w 6 1 joshua tree and the m w 7 3 landers earthquakes to quantify this change focal mechanisms from the 1975 galway lake sequence the 1979 homestead valley sequence background seismicity from 1981 to 1991 and the 1992 landers sequence are inverted for the state of stress in all cases the intermediate principal stress axis s2 remained vertical and changes in the state of stress consisted of variations in the trend of maximum and minimum principal stress axes s 1 and s 3 and small variations in the value of the relative stress magnitudes in general the stress state in the ecsz has s 1 trending east of north and 0 43 to 0 65 suggesting that the ecsz is a moderate stress refractor and the style of faulting is transtensional south of the pinto mountain fault in the region of the 1992 joshua tree earthquake the stress state determined from the 1981 to 1991 background seismicity changed on 23 april and again on 28 june 1992 in the central zone s 1 rotated from n14 5 e to n28 5 e on 23 april and back again to n16 5 e on 28 june thus the landers mainshock in effect recharged some of the shear stress in the region of the m w 6 1 joshua tree earthquake comparison of the state of stress before and after 28 june 1992 along the landers mainshock rupture zone showed that the mainshock changed the stress orientation the s1 trend rotated 7 to 20 clockwise and became progressively more fault normal from south to north along the emerson camp rock faults the variation was so prominent that the focal mechanisms of aftershocks could not be fit by a single deviatoric stress tensor the complex distribution of p and t axes suggests that most of the uniform component of the applied shear stress along the northern part of the rupture zone was released in the mainshock the san bernardino mountains region of the m w 6 2 big bear earthquake has a distinctively different state of stress as compared to the landers region with s 1 trending n3 5 w this region did not show any significant change in the state of stress following the 1992 m w 6 2 big bear sequence

high resolution seismic images and seismic velocities of the san andreas fault zone at burro flats southern california abstract to better understand the structure of the san andreas fault saf at burro flats in southern california we acquired a three dimensional combined set of seismic reflection and refraction profiles centered on the main active trace at burro flats in this article we discuss the variation in shallow depth velocities along each seismic profile with special emphasis on the 1500 m sec p wave velocity contour which can be an indicator of shallow depth water saturated unconsolidated sediments along the four seismic profiles minimum depths of the groundwater table as inferred from 1500 m sec velocity contour range from 10 to about 20 m the largest variations in depth to the top of the groundwater table occur in areas near mapped faults suggesting that the groundwater flow in burro flats is strongly affected by the locations of fault traces we also used the seismic data to develop seismic reflection images that show multiple strands of the saf in the upper 60 m reflectors above the 10 m depth probably correspond to holocene alluvial deposits reflectors below the 15 m depth probably arise from velocity or density variations within the precambrian gneiss complex likely due to weathering apparent vertical offsets of reflectors are observed along profiles lines 1 and 2 that are normal to the saf indicating minor apparent vertical offsets on the saf at shallow depths along line 2 the apparently vertically offset reflectors correlate with zones of relatively low p wave velocity along the central part of lines 1 and 2 the faults form a flower structure which is typical of strike slip faults such as the saf

an introductory perspective on non tropical shelf carbonates abstract this brief account introduces the topic of non tropical shelf carbonate deposits both modern and ancient specific aspects of which are described and discussed in the 22 accompanying papers in this special issue of sedimentary geology non tropical shelves are loosely defined as lying poleward of the present limit of development of hermatypic coral reefs or beyond the mean annual surface water isotherm of about 20 c typically near 30 latitude most geoscientists have traditionally regarded shallow water carbonate formation as a low latitude phenomenon however wherever the rate and extent of terrigenous sediment dilution is small the potential exists for extensive deposits of skeletal carbonate to accumulate on shelves beyond the sub tropics the facies attributes of the modern non tropical carbonates are distinctive and contrast significantly with the structural lithological faunal floral mineralogical and diagenetic character of their tropical counterparts in the rock record non tropical limestones probably occur throughout the phanerozoic but generally remain to be identified and or interpreted as such they are presently described mainly from the ordovician permian and tertiary quaternary periods of major continental glaciations and accentuated latitudinal thermal gradients a uniformitarian approach to the recognition and interpretation of ancient shallow marine limestones requires acceptance of both tropical and non tropical carbonate facies models

a budget of carbonate framework and sediment production kailua bay oahu hawaii abstract sediments of the bay and coastal plain of kailua oahu hawaii are 90 biogenic carbonate produced by destruction of primary reef framework coral and encrusting coralline algae and by direct sedimentation through the biological activity of calcifying organisms the green alga halimeda the branching coralline alga porolithion gardineri molluscs and benthic foraminifera field measurements of benthic community structure gross carbonate production bioerosion and direct sedimentation in 17 physiographic zones in kailua bay are used to calculate modern calcareous sediment production rates in the 12 km2 fringing reef system total gross carbonate productivity by corals and encrusting coralline algae based on mapped percent cover and known growth rates occurs at an average rate of 1 22 0 36 kg m 2 y 1 over hard substrates of the reef platform corresponding to 0 8 0 2 mm y 1 using a bulk density of 1 48 g cm 3 the average of coral and coralline algae coralline algae contributes 42 of the total gross productivity bioerosion of coral and coralline algae facies at and near the reef surface estimated from slabbed reef samples occurs at average rates of 0 10 1 15 kg m 2 y 1 and releases 1 911 436 m3 of unconsolidated carbonate sediment annually mechanical erosion coral breakage likely contributes an additional 315 m3 y 1 carbonate sediment is also produced directly by the green alga halimeda branching coralline algae molluscs and benthic foraminifera at a combined rate of 1 822 200 m3 y 1 using densities specific to sediment origin the total rate of production of unconsolidated carbonate sediment in kailua bay is the sum of these sources amounting to 4 048 635 m3 y 1 normalizing gross sediment production in kg y 1 by reef habitat area in m2 generates average rates of productivity in kg m 2 y 1 that are directly comparable to each other and to the literature such rates can also be employed and tested in other reef settings in kailua bay the total production of calcareous sediment corresponds to an average normalized rate of 0 53 0 19 kg m 2 y 1 with 0 33 0 13 kg m 2 y 1 contributed through erosion of the coralgal framework and 0 20 0 06 kg m 2 y 1 contributed by direct sediment production on the reef surface applying these modern sediment production rates over the 5 000 years that kailua bay has been completely inundated by postglacial sea level rise an estimated 20 2 3 2 106 m3 of unconsolidated carbonate sediment has been produced in the system the volume of sediment stored in the various reef channels and holes in kailua bay is 3 7 0 3 106 m3 or 19 of that produced since 5 000 y bp the volume of sand in the modern beach is 1 0 0 1 106 m3 or 5 of holocene sediment production the volume of carbonate sediment stored in the coastal plain is estimated using core log data and associated radiocarbon ages to be 10 0 1 8 106 m3 or 51 of holocene sediment production the remaining 25 likely represents sediment loss due to the natural processes of dissolution attrition and transport offshore these export terms are not well understood and emphasize the need for sediment dynamics to be incorporated into reef and sediment budgets although sediment production in this reef system is prodigious the rate of new sediment supplied to the beachface is less than 2 of what moves on and off the beach seasonally

sawtooth segmentation and deformation processes on the southern san andreas fault california five contiguous 12 13 km fault segments form a sawtooth geometry on the south ernmost san andreas fault the kinematic and morphologic properties of each segment depend on fault strike despite differences of strike between segments of as little as 3 degrees oblique slip transpression of fault segments within the indio hills mecca hills and durmid hill results from an inferred 8 1 ratio of dex tral slip to convergence across the fault zone triggered slip and creep are confined almost en tirely to transpressive segments of the fault durmid hill has been formed in the last 28 n 6 ka by uplift at an average rate of 3 1 mm a

nonlinear dimensional analysis of trapezoidal valleys subjected to vertically propagating sv waves this paper studies the seismic response of soil basins emphasizing the sensitivity of 2d dynamic response to geometric and material properties this is accomplished through a formal dimensional analysis accounting for fully inelastic soil response thus augmenting the generalization potential of the results and provid ing a novel framework for future research on the subject it is shown that 2d valley response may be described through the following key dimensionless parameters 1 the valley shape factor s expressing the slope inclination 2 the impedance ratio i which expresses the stiffness of the soil relative to the bedrock 3 the wavelength ratio s which is a function of soil stiffness and seismic excitation frequency 4 the rigidity ratio v expressing the stiffness of the soil relative to its strength and 5 the resistance ratio r which expresses the degree of soil nonlinearity the effectiveness of the dimensional formulation is verified through the numerical analysis of equivalent valleys assuming elastic and nonlinear soil response finally a parametric study is conducted to gain insight on the effects of the introduced dimensionless parameters on the dynamic response of trapezoidal alleys it is shown that decreasing thevalley slope or the wavelength ratio promotes wave reflections within the wedge thus enhancing the possibility of wave interferences and subsequently leading to 2d aggravation on the valley surface on the other hand the geometry dependent parasitic vertical accel eration increases as the valley slope becomes steeper as the degree of soil nonlinear ity increases 2d phenomena tend to become localized close to the valley edges

the 1992 landers earthquake sequence seismological observations the m w 6 1 7 3 6 2 1992 landers earthquakes began on april 23 with the m w6 1 1992 joshua tree preshock and form the most substantial earthquake sequence to occur in california in the last 40 years this sequence ruptured almost 100 km of both surficial and concealed faults and caused aftershocks over an area 100 km wide by 180 km long the faulting was predominantly strike slip and three main events in the sequence had unilateral rupture to the north away from the san andreas fault the m w6 1 joshua tree preshock at 33 n58 and 116 w19 on 0451 ut april 23 was preceded by a tightly clustered foreshock sequence m 4 6 beginning 2 hours before the mainshock and followed by a large aftershock sequence with more than 6000 aftershocks the aftershocks extended along a northerly trend from about 10 km north of the san andreas fault northwest of indio to the east striking pinto mountain fault the m w7 3 landers mainshock occurred at 34 n13 and 116 w26 at 1158 ut june 28 1992 and was preceded for 12 hours by 25 small m 3 earthquakes at the mainshock epicenter the distribution of more than 20 000 aftershocks analyzed in this study and short period focal mechanisms illuminate a complex sequence of faulting the aftershocks extend 60 km to the north of the mainshock epicenter along a system of at least five different surficial faults and 40 km to the south crossing the pinto mountain fault through the joshua tree aftershock zone towards the san andreas fault near indio the rupture initiated in the depth range of 3 6 km similar to previous m 5 earthquakes in the region although the maximum depth of aftershocks is about 15 km the mainshock focal mechanism showed right lateral strike slip faulting with a strike of n10 w on an almost vertical fault the rupture formed an arclike zone well defined by both surficial faulting and aftershocks with more westerly faulting to the north this change in strike is accomplished by jumping across dilational jogs connecting surficial faults with strikes rotated progressively to the west a 20 km long linear cluster of aftershocks occurred 10 20 km north of barstow or 30 40 km north of the end of the mainshock rupture the most prominent off fault aftershock cluster occurred 30 km to the west of the landers mainshock the largest aftershock was within this cluster the m w6 2 big bear aftershock occurring at 34 n10 and 116 w49 at 1505 ut june 28 it exhibited left lateral strike slip faulting on a northeast striking and steeply dipping plane the big bear aftershocks form a linear trend extending 20 km to the northeast with a scattered distribution to the north the landers mainshock occurred near the southernmost extent of the eastern california shear zone an 80 km wide more than 400 km long zone of deformation this zone extends into the death valley region and accommodates about 10 to 20 of the plate motion between the pacific and north american plates the joshua tree preshock its aftershocks and landers aftershocks form a previously missing link that connects the eastern california shear zone to the southern san andreas fault

slip on the superstition hills fault and on nearby faults associated with the 24 november 1987 elmore ranch and superstition hills earthquakes southern california alignment arrays and creepmeters spanning several faults in southern california recorded slip associated with the 24 november 1987 elmore ranch and superstition hills earthquakes no precursory slip had occurred on the superstition hills fault up to 27 october 1987 when the last measurement before the earthquakes was made about 23 days before the earthquake dextral creep events of about 13 mm and 0 5 mm may have occurred simultaneously on the imperial and southern san andreas faults respectively but the tectonic origin of the smaller event is questionable within 12 hr after the superstition hills earthquake 20 9 cm of dextral slip occurred on the main fault trace at the superstition hills alignment array and 39 8 cm of dextral slip was recorded over the entire 110 m width of the array despite this initial wide distribution of slip nearly all of the postseismic slip is occurring on the main fault trace as of 3 august 1988 the alignment array had recorded a total of 80 2 cm of dextral slip as of 5 days after the earthquakes 65 to 80 per cent of the total slip measured by the alignment array had occurred on discrete mappable fractures in addition the two earthquakes triggered slip on the coyote creek fault the southern san andreas fault and on the imperial fault telemetered data from creepmeters on the southern san andreas and imperial faults indicate that triggered slip began there within 3 min or less of each of the two earthquakes additional triggered slip occurred on the imperial fault beginning 3 5 hr after the second earthquake

lack of precursory slip to the 1999 hector mine california earthquake as constrained by insar we looked for evidence of interseismic strain occurring between the 1992 landers earthquake and the 1999 hector mine earthquake near the lavic lake and bullion faults by using interferometric synthetic aperture radar insar interferograms covering the hector mine epicentral region were studied for possible slip along the bullion and lavic lake faults by both visual inspection and a matched filter technique intended to emphasize slip located at the nucleation point some indications of possible deformation associated with the 5 july 1992 m l 5 4 pisgah event was observed but high decorrelation prevented a conclusive determination we have seen no evidence for precursory slip in the epicentral region up to 30 days before the hector mine event we estimated that the slip equivalent to a m w 4 5 event would have been observable in the months before the hector mine event and this places an upper bound on the long term precursory slip had it occurred we have noted that insar is well suited for detecting precursory slip in general due to the high spatial resolution and the lack of ground instrumentation required but that the detection level depends on the depth and orientation of the slip back

new slip along parts of the 1968 coyote creek fault rupture california on 28 and 30 november 1987 we found new surface ruptures along the central break of the coyote creek fault s 1968 rupture mapped slip that may have been triggered by the superstition hills earthquakes of 24 november 1987 was dominantly right lateral and ranged up to 15 mm total length of the new ruptures was about 3 km distributed along two quasi continuous segments of the main fault plus one segment of a secondary fault all of which ruptured in 1968 the longest segment of new rupture followed the northeast side of the ocotillo badlands for 2 3 km newly mapped slip in 1987 occurred along parts of the coyote creek fault that were characterized in 1968 by several features these were large total dextral slip a prominent vertical slip component rupture along single fractures instead of en echelon cracks and large afterslip in the few years following the 1968 earthquake past episodes of triggered slip on the san andreas imperial and superstition hills faults were hypothesized by others to be precursory phenomena the 1987 slip on the coyote creek fault however may be an episode of afterslip this suggestion is supported by the decrease in creep rates since 1968 shown by data from two alinement arrays on the coyote creek fault the correct interpretation of triggered slip events and their value as earthquake precursors therefore depends upon a good knowledge of the slip history of a fault

fault zone waves observed at the southern joshua tree earthquake rupture zone waveform and spectral characteristics of several aftershocks of the m 6 1 22 april 1992 joshua tree earthquake recorded at stations just north of the indio hills in the coachella valley can be interpreted in terms of waves propagating within narrow low velocity high attenuation vertical zones evidence for our interpretation consists of 1 emergent p arrivals prior to and opposite in polarity to the impulsive direct phase these arrivals can be modeled as headwaves indicative of a transfault velocity contrast 2 spectral peaks in the s wave train that can be interpreted as internally reflected low velocity fault zone wave energy and 3 spatial selectivity of event station pairs at which these data are observed suggesting a long narrow geologic structure the observed waveforms are modeled using the analytical solution of ben zion and aki 1990 for a plane parallel layered fault zone structure synthetic waveform fits to the observed data indicate the presence of ns trending vertical fault zone layers characterized by a thickness of 50 to 100 m a velocity decrease of 10 to 15 relative to the surrounding rock and a p wave quality factor in the range 25 to 50

large kelp rafted rocks as potential dropstones in the southern ocean abstract cyclonic winds in april 2017 forced oceanic kelp rafts onshore in southeastern new zealand providing a snapshot of ongoing kelp rock transport about 10 of observed southern bull kelp durvillaea antarctica holdfasts contain substantial remnants of their original rocky substrates the largest rock weighs 7 kg and was derived from the mesozoic sedimentary murihiku terrane of southern new zealand 100 km from the beach where it was deposited several other rafted rocks were derived from the same general source area including a conglomerate clast with 10 cm igneous cobbles genetic sequencing of the kelp specimens confirmed their southern new zealand derivation which is distinct from sub antarctic or northern new zealand clades the floating rocks had been colonised by goose barnacles lepas australis the largest of which were approximately 5 mm long implying that the rocks had been floating for approximately 16 days before being blown ashore the rocks may have travelled up to 200 km in that time in a northeasterly directed ocean current that flows at 10 15 km day if these rock bearing kelp rafts had not been blown ashore in the cyclonic weather event they would likely have continued to travel northeast in the subtropical front zone where they would likely have been deposited as dropstones abundant dropstones noted on the nearby chatham rise and campbell plateau have previously been assumed to have been ice rafted a component of these dropstones could have been derived by kelp rafting especially on the chatham rise where the subtropical front is deflected east a thick weathering rind and remnant organic veneer if present along with clast provenance may be the best distinguishing features of kelp rafted dropstones compared to ice rafted dropstones

kelp cobbles and currents biologic reduction of coarse grain entrainment stress models quantifying the onset of sediment motion do not typically account for the effect of biotic processes because they are difficult to isolate and quantify in relation to physical processes here we investigate an example of the interaction of kelp order laminariales and coarse sediment transport in the coastal zone where it is possible to directly quantify and test its effect kelp is ubiquitous along rocky coastlines and the impact on ecosystems has been well studied we develop a physical model to explore the reduction in critical shear stress of large cobbles colonized by nereocystis luetkeana or bull kelp observations of coarse sediment motion at a site in the strait of juan de fuca northwest united states canada boundary channel confirm the model prediction and show that kelp reduces the critical stress required for transport of a given grain size by as much as 92 enabling annual coarse sediment transport rates comparable to those of fluvial systems we demonstrate that biology is fundamental to the physical processes that shape the coastal zone in this setting

slip triggered on southern california faults by the 1992 joshua tree landers and big bear earthquakes five out of six functioning creepmeters on southern california faults recorded slip triggered at the time of some or all of the three largest events of the 1992 landers earthquake sequence digital creep data indicate that dextral slip was triggered within 1 min of each mainshock and that maximum slip velocities occurred 2 to 3 min later the duration of triggered slip events ranged from a few hours to several weeks we note that triggered slip occurs commonly on faults that exhibit fault creep to account for the observation that slip can be triggered repeatedly on a fault we propose that the amplitude of triggered slip may be proportional to the depth of slip in the creep event and to the available near surface tectonic strain that would otherwise eventually be released as fault creep we advance the notion that seismic surface waves perhaps amplified by sediments generate transient local conditions that favor the release of tectonic strain to varying depths synthetic strain seismograms are presented that suggest increased pore pressure during periods of fault normal contraction may be responsible for triggered slip since maximum dextral shear strain transients correspond to times of maximum fault normal contraction

refining the spatial and temporal signatures of creep and co seismic slip along the southern san andreas fault using very high resolution uas imagery and sfm derived topography coachella valley california abstract the current interseismic period for an event on the coachella valley segment of the san andreas fault saf is 300 years much greater than the best estimated average recurrence interval of 180 years prompting questions regarding earthquake recurrence and fault behavior digital surface models dsms generated using structure from motion multiview stereo sfm mvs techniques on unmanned aerial systems uas imagery and very high resolution uas orthomosaics were used to identify and measure fault related offsets of small geomorphic features and develop a model of late holocene slip per event for the southern saf ssaf in the coachella valley we aim to better constrain slip estimates from recent earthquakes along the ssaf and combine new slip data with ages of past earthquakes from paleoseismic studies to understand earthquake recurrence slip per event for paleoearthquakes which ruptured this segment of the ssaf and the relationship between co seismic slip events creep or afterslip and triggered slip were evaluated examination of offsets suggests that five 5 large surface rupturing events produced average displacements of 2 6 3 1 m per event gaussian distribution analysis revealed small scale offset clusters that we attribute to climate modulated channel incision across the fault and subsequent creep these offset clusters support a creep rate of 3 mm yr in the mecca hills averaged over the past 160 years

recent observations of the mean circulation on georges bank abstract a clockwise circulation around georges bank was measured by means of moored current meters aircraft tracked surface drifters and satellite tracked drifters drogued at 10 m the strongest flow was in a narrow jetlike current 30 cm s 1 along the northern flank of the bank the flow of shelf water on the southern flank was westward 10 cm s 1 toward the middle atlantic bight some of this water flowed northward through the eastern side of great south channel and recirculated around georges bank the satellite tracked drifters and the moored observations indicate that the circulation around the bank was not completely closed and considerable variability occurs in the trajectory of an individual water particle

near field investigations of the landers earthquake sequence april to july 1992 the landers earthquake which had a moment magnitude m w of 7 3 was the largest earthquake to strike the contiguous united states in 40 years this earthquake resulted from the rupture of five major and many minor right lateral faults near the southern end of the eastern california shear zone just north of the san andreas fault its m w 6 1 preshock and m w 6 2 aftershock had their own aftershocks and foreshocks surficial geological observations are consistent with local and far field seismologic observations of the earthquake large surficial offsets as great as 6 meters and a relatively short rupture length 85 kilometers are consistent with seismological calculations of a high stress drop 200 bars which is in turn consistent with an apparently long recurrence interval for these faults