the accommodation of the south flank s motion by the koa e fault system kīlauea hawai i insights from the june 2012 earthquake sequence

resonant slow fault slip in subduction zones forced by climatic load stress global positioning system gps measurements at subduction plate boundaries often record fault movements similar to earthquakes but much slower occurring over timescales of 1 week to 1 year these slow slip events have been observed in japan1 2 cascadia3 4 5 6 7 mexico8 9 alaska10 and new zealand11 the phenomenon is poorly understood but several observations hint at the processes underlying slow slip although slip itself is silent seismic instruments often record coincident low amplitude tremor in a narrow 1 5 cycles per second frequency range12 also modelling of gps data3 7 9 and estimates of tremor location13 indicate that slip focuses near the transition from unstable stick slip to stable friction at the deep limit of the earthquake producing seismogenic zone perhaps most intriguingly slow slip is periodic at several locations with recurrence varying from 6 to 18 months depending on which subduction zone or even segment is examined4 5 6 9 here i show that such periodic slow fault slip may be a resonant response to climate driven stress perturbations fault slip resonance helps to explain why slip events are periodic why periods differ from place to place and why slip focuses near the base of the seismogenic zone resonant slip should initiate within the rupture zone of future great earthquakes suggesting that slow slip may illuminate fault properties that control earthquake slip

volcano tectonic implications of 3 d velocity structures derived from joint active and passive source tomography of the island of hawaii 1 we present a velocity model of the onshore and offshore regions around the southern part of the island of hawaii including southern mauna kea southeastern hualalai and the active volcanoes of mauna loa and kilauea and loihi seamount the velocity model was inverted from about 200 000 first arrival traveltime picks of earthquakes and air gun shots recorded at the hawaiian volcano observatory hvo reconstructed volcanic structures of the island provide us with an improved understanding of the volcano tectonic evolution of hawaiian volcanoes and their interactions the summits and upper rift zones of the active volcanoes are characterized by high velocity materials correlated with intrusive magma cumulates these high velocity materials often do not extend the full lengths of the rift zones suggesting that rift zone intrusions may be spatially limited seismicity tends to be localized seaward of the most active intrusive bodies low velocity materials beneath parts of the active rift zones of kilauea and mauna loa suggest discontinuous rift zone intrusives possibly due to the presence of a preexisting volcanic edifice e g along mauna loa beneath kilauea s southwest rift zone or alternatively removal of high velocity materials by large scale landsliding e g along mauna loa s western flank both locations also show increased seismicity that may result from edifice interactions or reactivation of buried faults new high velocity regions are recognized and suggest the presence of buried and in some cases previously unknown rift zones within the northwest flank of mauna loa and the south flanks of mauna loa hualalai and mauna kea

tremor genic slow slip regions may be deeper and warmer and may slip slower than non tremor genic regions slow slip events sses are observed worldwide and often coincide with tectonic tremor notable examples of sses lacking observed tectonic tremor however occur beneath k lauea volcano hawaii the boso peninsula japan near san juan bautista on the san andreas fault california and recently in central ecuador these sses are similar to other worldwide sses in many ways e g size or duration but lack the concurrent tectonic tremor observed elsewhere instead they trigger swarms of regular earthquakes we investigate the physical conditions that may distinguish these non tremor genic sses from those associated with tectonic tremor including slip velocity pressure temperature fluids and fault asperities although we cannot eliminate the possibility that tectonic tremor may be obscured in highly attenuating regions slip velocities of sses at k lauea volcano 10 6 m s and boso peninsula 10 7 m s are among the fastest sses worldwide k lauea volcano the boso peninsula and central ecuador are also among the shallowest sses worldwide and thus have lower confining pressures and cooler temperatures in their respective slow slip zones fluids also likely contribute to tremor generation and no corresponding zone of high vp vs has been noted at k lauea or boso we suggest that the relatively faster slip velocities at k lauea volcano and the boso peninsula result from specific physical conditions that may also be responsible for triggering swarms of regular earthquakes adjacent to the slow slip while different conditions produce slower sse velocities elsewhere and trigger tectonic tremor

comparative velocity structure of active hawaiian volcanoes from 3 d onshore offshore seismic tomography abstract we present a 3 d p wave velocity model of the combined subaerial and submarine portions of the southeastern part of the island of hawaii based on first arrival seismic tomography of marine airgun shots recorded by the onland seismic network our model shows that high velocity materials 6 5 7 0 km s lie beneath kilauea s summit koae fault zone and the upper southwest rift zone swrz and upper and middle east rift zone erz indicative of magma cumulates within the volcanic edifice a separate high velocity body of 6 5 6 9 km s within kilauea s lower erz and upper puna ridge suggests a distinct body of magma cumulates possibly connected to the summit magma cumulates at depth the two cumulate bodies within kilauea s erz may have undergone separate ductile flow seaward influencing the submarine morphology of kilauea s south flank low velocities 5 0 6 3 km s seaward of kilauea s hilina fault zone and along mauna loa s seaward facing kao iki fault zone are attributed to thick piles of volcaniclastic sediments deposited on the submarine flanks loihi seamount shows high velocity anomalies beneath the summit and along the rift zones similar to the interpreted magma cumulates below mauna loa and kilauea volcanoes and a low velocity anomaly beneath the oceanic crust probably indicative of melt within the upper mantle around kilauea s submarine flank a high velocity anomaly beneath the outer bench suggests the presence of an ancient seamount that may obstruct outward spreading of the flank mauna loa s southeast flank is also marked by a large anomalously high velocity feature 7 0 7 4 km s interpreted to define an inactive buried volcanic rift zone which might provide a new explanation for the westward migration of mauna loa s current swrz and the growth of kilauea s swrz

repeating earthquakes as low stress drop events at a border between locked and creeping fault patches the source of repeating earthquakes on creeping faults is modeled as a weak asperity at a border between much larger locked and creeping patches on the fault plane the x 1 2 decrease in stress concentration with distance x from the boundary is shown to lead directly to the observed scaling t m 1 6 between the average repeat time and average scalar moment for a repeating sequence the stress drop in such small events at the border depends on the size of the large locked patch for a circular patch of radius r and representative fault parameters 7 6 m r 3 5 mpa which yields stress drops between 0 08 and 0 5 mpa 0 8 5 bars for r between 2 km and 100 m these low stress drops are consistent with estimates of stress drop for small earthquakes based on their seismic spectra however they are orders of magnitude smaller than stress drops calculated under the assumption that repeating sources are isolated stuck asperities on an otherwise creeping fault plane whose seismic slips keep pace with the surrounding creep rate linear streaks of microearthquakes observed on creeping fault planes are trivially explained by the present model as alignments on the boundaries between locked and creeping patches

detecting aseismic strain transients from seismicity data 1 aseismic deformation transients such as fluid flow magma migration and slow slip can trigger changes in seismicity rate we present a method that can detect these seismicity rate variations and utilize these anomalies to constrain the underlying variations in stressing rate because ordinary aftershock sequences often obscure changes in the background seismicity caused by aseismic processes we combine the stochastic epidemic type aftershock sequence model that describes aftershock sequences well and the physically based rate and state dependent friction seismicity model into a single seismicity rate model that models both aftershock activity and changes in background seismicity rate we implement this model into a data assimilation algorithm that inverts seismicity catalogs to estimate space time variations in stressing rate we evaluate the method using a synthetic catalog and then apply it to a catalog of m 1 5 events that occurred in the salton trough from 1990 to 2009 we validate our stressing rate estimates by comparing them to estimates from a geodetically derived slip model for a large creep event on the obsidian buttes fault the results demonstrate that our approach can identify large aseismic deformation transients in a multidecade long earthquake catalog and roughly constrain the absolute magnitude of the stressing rate transients our method can therefore provide a way to detect aseismic transients in regions where geodetic resolution in space or time is poor

monitoring aseismic forcing in fault zones using earthquake time series the dynamics of earthquake occurrences is controlled both by fault in teraction processes and by long term tectonic loading of the faults in addition tran sient loading can be caused by aseismic deformation episodes for example during crustal fluid migration or slow slip events these forcing transients are best revealed by geodetic measurements however this type of instrumentation is not always avail able or is not always sensitive enough to detect significant anomalies in such cases one is better off exploiting the seismicity signature of these transients in order to char acterize them we here explore different ways to do so interearthquake time statistics are found to be prone to damping out fluctuations in forcing rate a more accurate method is developed by comparing the data with a triggering model that accounts for earthquake interactions the changes in fault loading rates are then well recovered both in duration and in intensity

rapid deformation of kilauea volcano global positioning system measurements between 1990 and 1996 campaign global positioning system gps measurements from 1990 to 1996 are used to calculate surface displacement rates on kilauea volcano hawaii the gps data show that the south flank of the volcano which has generated several large earthquakes in the past 3 decades is displacing at up to 8 cm yr to the south southeast the summit and rift zones are subsiding with maximum subsidence rates of 8 cm yr observed a few kilometers south of the summit caldera elastic dislocation modeling of the gps data suggests that the active sources of deformation include deep rift opening along the upper east and east rift zone fault slip along a subhorizontal fault near the base of the volcano and deflation near the summit caldera a nonlinear optimization algorithm was used to explore the parameter space and to find the best fitting source geometry there is a broad range of model geometries that fit the data reasonably well however certain models can be ruled out including those that have shallow rift opening or shallow fault slip some offshore aseismic slip on a fault plane that dips between 258 north northwest and 88 south southeast is required best fitting slip and rift opening rates are 23 28 cm yr although rates as low as 10 cm yr are permitted by the data

the use of earthquake rate changes as a stress meter at kilauea volcano stress changes in the earth s crust are generally estimated from model calculations that use near surface deformation as an observational constraint but the widespread correlation of changes of earthquake activity with stress has led to suggestions that stress changes might be calculated from earthquake occurrence rates obtained from seismicity catalogues although this possibility has considerable appeal because seismicity data are routinely collected and have good spatial and temporal resolution the method has not yet proven successful owing to the non linearity of earthquake rate changes with respect to both stress and time here however we present two methods for inverting earthquake rate data to infer stress changes using a formulation for the stress and time dependence of earthquake rates application of these methods at kilauea volcano in hawaii yields good agreement with independent estimates indicating that earthquake rates can provide a practical remote sensing stress meter

focused seismicity triggered by flank instability on kīlauea s southwest rift zone abstract swarms of earthquakes at the head of the southwest rift zone on k lauea volcano hawai i reveal an interaction of normal and strike slip faulting associated with movement of k lauea s south flank a relocated subset of earthquakes between january 2012 and august 2014 are highly focused in space and time at depths that are coincident with the south caldera magma reservoir beneath the southern margin of k lauea caldera newly calculated focal mechanisms are dominantly dextral shear with a north south preferred fault orientation two earthquakes within this focused area of seismicity have normal faulting mechanisms indicating two mechanisms of failure in very close proximity 10 s of meters to 100 m we suggest a model where opening along the southwest rift zone caused by seaward motion of the south flank permits injection of magma and subsequent freezing of a plug which then fails in a right lateral strike slip sense consistent with the direction of movement of the south flank the seismicity is concentrated in an area where a constriction occurs between a normal fault and the deeper magma transport system into the southwest rift zone although in many ways the southwest rift zone appears analogous to the more active east rift zone the localization of the largest seismicity m2 5 within the swarms to a small volume necessitates a different model than has been proposed to explain the lineament outlined by earthquakes along the east rift zone

double difference tomography the method and its application to the hayward fault california we have developed a double difference dd seismic tomography method that makes use of both absolute and relative arrival times by reducing systematic errors using the more accurate relative arrival times the method produces an improved velocity model simultaneously it yields event locations of a quality equivalent to those of the dd location method while avoiding simplifying assumptions of that method we test this method on a synthetic dataset and find that it produces a more accurate velocity model and event locations than standard tomography we also test this method on a hayward fault california earthquake dataset spanning 1984 1998 the earthquakes relocated by this method collapse to a thin line along the fault trace consistent with previous results the dd velocity model has sharper velocity contrasts near the source region than the standard tomography model

new insights into kilauea s volcano dynamics brought by large scale relative relocation of microearthquakes 1 we investigated the microseismicity recorded in an active volcano to infer information concerning the volcano structure and long term dynamics by using relative relocations and focal mechanisms of microearthquakes there were 32 000 earthquakes of the mauna loa and kilauea volcanoes recorded by more than eight stations of the hawaiian volcano observatory seismic network between 1988 and 1999 we studied 17 000 of these events and relocated more than 70 with an accuracy ranging from 10 to 500 m about 75 of these relocated events are located in the vicinity of subhorizontal decollement planes at a depth of 8 11 km however the striking features revealed by these relocation results are steep southeast dipping fault planes working as reverse faults clearly located below the decollement plane and which intersect it if this decollement plane coincides with the pre mauna loa seafloor as hypothesized by numerous authors such reverse faults rupture the pre mauna loa oceanic crust the weight of the volcano and pressure in the magma storage system are possible causes of these ruptures fully compatible with the local stress tensor computed by gillard et al 1996 reverse faults are suspected of producing scarps revealed by kilometer long horizontal slip perpendicular lineations along the decollement surface and therefore large scale roughness asperities and normal stress variations these are capable of generating stick slip large magnitude earthquakes the spatial microseismic pattern observed in the south flank of kilauea volcano and hilina type instabilities rupture intersecting the decollement surface causing its large scale roughness may be an important parameter controlling the growth of hawaiian volcanoes

earthquake swarms in circum pacific subduction zones abstract we systematically and manually search through clusters of earthquakes along circum pacific subduction zones to identify potential earthquake swarms in total we find 266 potential earthquake swarms 180 we classify as megathrust and 68 we classify as volcanic due to their proximity to the megathrust or to volcanoes we focus on the megathrust swarms and demonstrate that 1 the number of events in a swarm is not a function of the largest earthquake in the swarm 2 swarms exhibit an approximately constant rate of seismicity that lasts until after the mean timing of events in the swarm 3 the timing of the largest earthquake in the sequence is no different than the timing of any other earthquake in the sequence 4 our catalogs of earthquakes comprising swarms 9000 events have high b values 1 5 to 2 and 5 when earthquake swarms are considered as single events using total duration and cumulative moment they appear to be consistent with the slow earthquake magnitude duration scaling law presented by ide et al 2007 the first three observations along with the observation that swarms can span very large areas compared to their cumulative seismic moment argue against static stress triggering as a driving mechanism for earthquake swarms along strike propagation velocities are observed for several swarms showing epicentral propagation of 10 km day similar to other documented slow slip events together this evidence implies that aseismic slip along the megathrust is likely an important mechanism for the generation of megathrust earthquake swarms in circum pacific subduction zones we then conduct a comparison of swarms and large megathrust earthquakes finding evidence that the two are broadly anti correlated megathrust segments with large earthquake swarm gaps are more likely to experience large mw 8 megathrust events we characterize the ubiquity of megathrust swarms at different margins and suggest that fault properties along marianas type margins may allow for earthquake swarms to occur regularly but other margins may rely on other variables such as the subduction of a ridge or seamount to facilitate the generation of megathrust earthquake swarms

characteristics of deep 13 km hawaiian earthquakes and hawaiian earthquakes west of 155 55 w 1 high precision relocation of earthquakes recorded by the hawaiian volcano observatory hvo seismic network provides new information on the characteristics of seismic faulting at this oceanic hot spot using waveform cross correlation we have measured correlation coefficients and travel time differences for a set of 14 605 deep 13 km earthquakes recorded from 1988 to 1998 we find that about half of the analyzed earthquakes are in similar event clusters that delineate fault zones in the lower crust and upper mantle we suggest that much of this deep seismicity reflects rupture in the brittle lithosphere away from the magma pathways although at kilauea the stresses from magma movement may additionally help trigger mantle earthquakes on preexisting faults in regions with high differential ambient stresses focal mechanisms of similar event clusters throughout hawaii display characteristic patterns and appear consistent with the hypothesis that deep earthquakes on preexisting faults reflect the stresses due to volcano loading and flexure we also present the results of applying cross correlation analyses and relocation to 7000 earthquakes at all depths located west of 155 55 w and recorded from 1988 to 1998 the pattern of relocated earthquakes at the kealakekua fault zone is consistent with the presence of a low angle detachment on the west flank of mauna loa

slow slip and tremor search at kilauea volcano hawaii 1 kilauea volcano hawaii has hosted a long series of slow slip events observed since the installation of the continuous gps network in 1996 kilauea s slow slip events are inferred to occur on the decollement fault at 8 km depth beneath its south flank with a location updip of the epicenters of large regular earthquakes fault slip typically lasts about two days and the events have magnitudes equivalent to mw 5 3 6 0 while slow slip events in subduction zones are commonly accompanied by tectonic tremor also called nonvolcanic tremor no tremor has yet been reported in association with kilauea s slow slip events instead there are swarms of small triggered earthquakes which is a characteristic only seen at select subduction zones e g boso and hikurangi a temporary array of seismometers was installed at kilauea in 2007 in anticipation of a slow slip event here we use several established methods to perform a systematic search for tectonic tremor during geodetically defined slow slip events as well as searching for tremor triggered by teleseismic surface waves we do not detect tectonic tremor using any of these methods although we are able to detect episodes of previously identified deep offshore volcanic tremor at 15 20 km depth and volcanic tremor from kilauea although kilauea s seismic network may not be adequate to observe tectonic tremor because hawaii is seismically noisy and its crust is highly attenuating it is also possible that the specific fault conditions on kilauea s decollement are not conducive to such tremor generation

erratum earthquakes triggered by silent slip events on kīlauea volcano hawaii nature 442 71 74 2006 there was a plotting error in fig 1 that inadvertently displays earthquakes for the incorrect time interval the location of earthquakes during the two day long slow slip event of january 2005 are shown here in the corrected fig 1 because the incorrect locations were alsoused in the coulomb stress change csc calculation the error could potentially have biased our interpretation of the depth of the slow slip event although in fact it did not

kilauea slow slip events identification source inversions and relation to seismicity 1 several slow slip events beneath the south flank ofkilauea volcano hawaii have been inferred from transient displacements in daily gps positions to search for smaller events that may be close to the noise level in the gps time series we compare displacement fields on kilauea s south flank with displacement patterns in previously identified slow slip events matching displacement patterns are found for several new candidate events although displacements are much smaller than previously identified events one of the candidates 29 may 2000 is coincident with a microearthquake swarm as are all of the previously identified slow slip events the microearthquakes follow the onset of slow slip implying that they are triggered by stress changes during slip the new slow slip event brings the total number of events on kilauea between 1997 and 2007 to eight the smallest having m w 5 3 and the largest having m w 6 0 while the recurrence time between the four largest events is 2 11 0 01 years the repeat time for all eight events is 0 9 0 6 years we invert for the fault geometry and distribution of slip during the slow slip events the optimal source depths of 5 km assuming uniform slip dislocations in an elastic half space are considerably shallower than the accompanying swarm earthquakes 6 5 8 5 km which would place the earthquakes in a zone of decreased coulomb stress inversions including the effects of topography and layered elastic structure in the forward models favor depths comparable to microearthquake depths such that the earthquakes are located in a region of increased coulomb stress we also invert for time dependent fault slip directly from the 30 s gps phase observations constraining the source to the optimal uniform slip geometry on the basis of these inversions the larger events last between 1 5 2 2 days the data are unable to resolve migration of slip along the fault the temporal pattern of accompanying microearthquakes is consistent with the fault slip history assuming a seismicity rate theory based on rate and state friction making the swarm earthquakes coshocks and aftershocks of the slow slip events

seismic evidence for a crustal magma reservoir beneath the upper east rift zone of kilauea volcano hawaii an anomalous body with low vp compressional wave velocity low vs shear wave velocity and high vp vs anomalies is observed at 8 11 km depth beneath the upper east rift zone of kilauea volcano in hawaii by simultaneous inversion of seismic velocity structure and earthquake locations we interpret this body to be a crustal magma reservoir beneath the volcanic pile similar to those widely recognized beneath mid ocean ridge volcanoes combined seismic velocity and petrophysical models suggest the presence of 10 melt in a cumulate magma mush this reservoir could have supplied the magma that intruded into the deep section of the east rift zone and caused its rapid expansion following the 1975 m7 2 kalapana earthquake

the 2010 slow slip event and secular motion at kilauea hawai i inferred from terrasar x insar data we present here a small baseline subset sbas algorithm to extract both transient and secular ground deformations on the order of millimeters in the presence of tropospheric noise on the order of centimeters when the transient is of short duration and known time and the background deformation is smooth in time we applied this algorithm to study the 2010 slow slip event as well as the secular motion of kilauea s south flank using 49 terrasar x images we also estimate the tropospheric delay variation relative to a given reference pixel using an interferometric synthetic aperture radar insar sbas approach we compare the insar sbas solution for both ground deformation and tropospheric delays with existing gps measurements and confirm that the ground deformation signal and tropospheric noise in insar data are successfully separated we observe that the coastal region on the south side of the hilina pali moves at a higher background rate than the region north side of the pali we also conclude that the 2010 slow slip event sse displacement is mainly horizontal and the maximum magnitude of the 2010 sse vertical component is less than 5 mm

observations of event based streambed deformation in a gravel bed channel 1 the streambed is the major source of bed load sediment in gravel bed channels and is necessarily deformed during floods that mobilize sediment this study uses observations of scour and fill from carnation creek canada to articulate at a point relations of the occurrence and magnitude of bed deformation and the resulting adjustments in bed configuration over a series of flood events the likelihood of local bed deformation by scour fill or both depends on flow magnitude at most locations there is an imbalance of scour and fill that leads to adjustments in bed elevation and these imbalances increase with flow persistent deformation of locations in lower portions of the bed topography tend to produce larger total exchanges between bed and mobile sediment over the flood series but locations that experience similar frequencies of bed deformation do not produce unique depth distributions these results underscore the importance of understanding the coupling of scour and fill that produces streambed adjustment when modeling streambed evolution and managing river habitat

overthrusting and sediment accretion along kilauea s mobile south flank hawaii evidence for volcanic spreading from marine seismic reflection data a large intermittently active submarine landslide known as the hilina slump has been interpreted along the south flank of kilauea volcano seaward dipping faults on land mark its headwall and an offshore bench may define its uplifted toe geodetic data show that the entire south flank is also moving seaward by a process referred to as volcanic spreading this provides an alternative explanation for the bench i e overthrusting along the edge of the sliding flank the latter interpretation is consistent with new seismic reflection data across the submarine flank a prominent reflection near the top of the oceanic plate suggests the decollement upon which the mobile flank slides landward dipping reflections rise from this horizon and bound packages of bedded strata faulted and imbricated within the bench the absence of correlative seaward dipping faults and rotated strata on the upper flank suggests that the bench is not coupled to a slump moreover kinematic reconstructions of the bench indicate that it has accommodated 15 24 km of displacement this value is consistent with estimates for rift zone extension but too high for shortening at the toe of a slump we interpret the bench to result from overthrusting and accretion of volcaniclastic sediments to the edge of the mobile flank and suggest that morphologic benches develop preferentially where landslide debris has accumulated near the base of the volcano and can be accreted to its sliding edifice

aseismic slip transients emerge spontaneously in three dimensional rate and state modeling of subduction earthquake sequences 1 to investigate the possible physical mechanisms of recently observed aseismic slip events in the cascadia japan and mexico subduction zones we apply a dieterich ruina rate and state friction law to a three dimensional model of a shallow subduction fault that is loaded by imposed steady plate slip rate far downdip along the thrust interface friction properties are temperature and hence depth dependent such that sliding is stable at depths below about 30 km the system is perturbed into a significantly nonuniform slip mode along strike by introducing small along strike variations in the constitutive parameters a and a b in addition to large heterogeneous earthquake slip at seismogenic depths and associated postseismic transients we found that slip events which have clearly aseismic slip rates emerge spontaneously around the downdip end of the seismogenic zone both transients which start well after a seismic event and those which are triggered by other transients are observed from the simulations the slip velocity depth range and sometimes along strike migration speed of simulated transients are similar to the observations from natural subduction zones unstable stable transitional friction properties near the downdip end of the seismogenic zone are suggested to be an ingredient allowing such transients simulated transients can weaken the locking intensity of the updip seismogenic zone while enhancing that of the transition zone spatial temporal correlation of aseismic transients and nearby seismicity in the guerrero mexico area suggests that transients may signal a period of increased probability for nucleating their high frequency counterparts as damaging subduction thrust events

earthquakes triggered by silent slip events on kīlauea volcano hawaii silent earthquakes or slow slip events happen so slowly that they cannot be detected by conventional seismographs but now the availability of gps data means that they can be followed in detail segall et al report on a series of small earthquakes on k lauea volcano hawaii the earthquakes at depths of 7 to 8 km appear to be triggered by otherwise silent slow slips though small triggered earthquakes of this type can be used to help quantify the increased hazard due to slow slip events slow slip events or silent earthquakes have recently been discovered in a number of subduction zones including the nankai trough1 2 3 in japan cascadia4 5 and guerrero6 in mexico but the depths of these events have been difficult to determine from surface deformation measurements although it is assumed that these silent earthquakes are located along the plate megathrust this has not been proved slow slip in some subduction zones is associated with non volcanic tremor7 8 but tremor is difficult to locate and may be distributed over a broad depth range9 except for some events on the san andreas fault10 slow slip events have not yet been associated with high frequency earthquakes which are easily located here we report on swarms of high frequency earthquakes that accompany otherwise silent slips on k lauea volcano hawaii for the most energetic event in january 2005 the slow slip began before the increase in seismicity the temporal evolution of earthquakes is well explained by increased stressing caused by slow slip implying that the earthquakes are triggered the earthquakes located at depths of 7 8 km constrain the slow slip to be at comparable depths because they must fall in zones of positive coulomb stress change triggered earthquakes accompanying slow slip events elsewhere might go undetected if background seismicity rates are low detection of such events would help constrain the depth of slow slip and could lead to a method for quantifying the increased hazard during slow slip events because triggered events have the potential to grow into destructive earthquakes

seismic velocity and attenuation structure of the east rift zone and south flank of kilauea volcano hawaii it has been proposed that a deep magma body beneath the east rift zone erz of kilauea volcano hawaii must be present in order to explain the observed deformation of the south flank from november 1999 to june 2000 29 iris passcal three component seismographs were operated across kilauea9s erz and south flank using local earthquakes recorded by these stations supplemented with data from the hawaiian volcano observatory stations we investigated the deep structure of the erz and south flank through two approaches seismic velocity tomography and seismic attenuation tomography results along two north northwest south southeast profiles are examined the western profile shows a low velocity region beneath and south of the hilina pali and earthquakes at depth are sandwiched between a high v p v s high q zone and a low v p v s low q zone the velocity and attenuation differences are interpreted to reflect the contrast in material properties between the overlying volcanic pile and the underlying fluid rich ocean sediments and fractured altered ocean crust beneath the south flank thrust fault the eastern profile shows an anomalous feature with low v p low v p v s high q p and low q s at about 7 km depth beneath the erz the low v p v s ratio is inconsistent with the presence of partial melt instead this anomaly is attributed to a trapped reservoir of co 2 our results do not support the existence of a sizable molten or partially molten body at depth beneath the erz if the deep magma body exists it must be relatively small based on synthetic resolution tests an estimated limit on the maximum allowable cross sectional size of the deep magma body is about 2 by 4 km

microearthquake streaks and seismicity triggered by slow earthquakes on the mobile south flank of kilauea volcano hawai i 1 we perform waveform cross correlation and high precision relocation of both background seismicity and seismicity triggered by periodic slow earthquakes at kilauea volcano s mobile south flank we demonstrate that the triggered seismicity dominantly occurs on several preexisting fault zones at the hilina region regardless of the velocity model employed the relocated earthquake epicenters and triggered seismicity localize onto distinct fault zones that form streaks aligned with the slow earthquake surface displacements determined from gps due to the unknown effects of velocity heterogeneity and nonideal station coverage our relocation analyses cannot distinguish whether some of these fault zones occur within the volcanic crust at shallow depths or whether all occur on the decollement between the volcano and preexisting oceanic crust at depths of 8 km nonetheless these hilina fault zones consistently respond to stress perturbations from nearby slow earthquakes

the unusual early morning tornado in ciudad acuna coahuila mexico on 25 may 2015 abstractthis study analyzes the synoptic and mesoscale conditions present during initiation and intensification of the supercell thunderstorm that produced a tornado in ciudad acuna a community located in the state of coahuila mexico 10 km southwest of the u s border early morning convective activity first detected by radar at 0628 utc 25 may 2015 developed into an intense and well defined supercell thunderstorm that produced a tornado between approximately 1045 and 1130 utc hourly analyses from the rapid refresh model indicated an upslope component to surface flow in the region of convection initiation over the serranias del burro sdb along the storm s trajectory dewpoint temperatures increased from 15 to 22 c convective available potential energy increased from 1500 to near 4000 j kg 1 and convective inhibition changed from 150 j kg 1 at the time of convection initiation to near zero in ciudad acuna simulations from the weather research and forecasting model confirmed the sensitivity o

earthquake swarms and slow slip on a sliver fault in the mexican subduction zone the mexican subduction zone is an ideal location for studying subduction processes due to the short trench to coast distances that bring broad portions of the seismogenic and transition zones of the plate interface inland using a recently generated seismicity catalog from a local network in oaxaca we identified 20 swarms of earthquakes m

interaction of slip on asperities numerical simulation of seismic cycles on a two dimensional planar fault with nonuniform frictional property 1 numerical simulation is conducted to understand the variety of frictional sliding on a plate interface and complex recurrence of earthquakes a planar square fault in an infinite uniform elastic medium is considered and the frictional stress on the fault is assumed to obey a rate and state dependent friction law nonuniformity in a frictional constitutive parameter is introduced on the model fault on the fault plane one or two circular patches with velocity weakening frictional property are surrounded by velocity strengthening areas unstable slip may occur for velocity weakening friction and aseismic sliding occurs for velocity strengthening friction velocity weakening patches correspond to asperities because intense seismic slip may occur there simulation results indicate that episodic aseismic slip events slow earthquakes occur when the velocity weakening patch size is close to the critical size of earthquake nucleation propagation of postseismic sliding on the velocity strengthening region follows an earthquake at a velocity weakening patch when the postseismic sliding reaches another velocity weakening patch an earthquake may be triggered at the patch resulting in a double earthquake the time delay between two events of the double earthquake increases with the distance between the two velocity weakening patches or the degree of velocity strengthening in the region between the patches when the distance between the two velocity weakening patches is long an earthquake at one patch does not directly cause an earthquake at the other patch in these cases complex earthquake recurrence may appear due to the interaction between ruptures at the two patches and the recurrence interval of earthquakes and coseismic slip is not constant at each velocity weakening patch

geodetic evidence for en echelon dike emplacement and concurrent slow slip during the june 2007 intrusion and eruption at kīlauea volcano hawaii 1 a series of complex events at k lauea volcano hawaii 17 june to 19 june 2007 began with an intrusion in the upper east rift zone erz and culminated with a small eruption 1500 m3 surface deformation due to the intrusion was recorded in unprecedented detail by global positioning system gps and tilt networks as well as interferometric synthetic aperture radar insar data acquired by the envisat and alos satellites a joint nonlinear inversion of gps tilt and insar data yields a deflationary source beneath the summit caldera and an ene striking uniform opening dislocation with 2 m opening a dip of 80 to the south and extending from the surface to 2 km depth this simple model reasonably fits the overall pattern of deformation but significantly misfits data near the western end of an inferred dike like source three more complex dike models are tested that allow for distributed opening including 1 a dike that follows the surface trace of the active rift zone 2 a dike that follows the symmetry axis of insar deformation and 3 two en echelon dike segments beneath mapped surface cracks and newly formed steaming areas the en echelon dike model best fits near field gps and tilt data maximum opening of 2 4 m occurred on the eastern segment beneath the eruptive vent although this model represents the best fit to the erz data it still fails to explain data from a coastal tiltmeter and gps sites on k lauea s southwestern flank the southwest flank gps sites and the coastal tiltmeter exhibit deformation consistent with observations of previous slow slip events beneath k lauea s south flank but inconsistent with observations of previous intrusions slow slip events at k lauea and elsewhere are thought to occur in a transition zone between locked and stably sliding zones of a fault an inversion including slip on a basal decollement improves fit to these data and suggests a maximum of 15 cm of seaward fault motion comparable to previous slow slip events