Triggered Waves Research Articles

Frequency dependence of delayed and instantaneous triggering on laboratory and simulated faults governed by rate‐state friction

AbstractEarthquake triggering by transient stresses is commonly observed; however, some aspects remain unexplained. The first is the often‐observed delay between the triggered earthquakes and the triggering waves, and the second is the unexpected effectiveness of transient stressing in the seismic frequency band. Previous theoretical and laboratory studies have suggested that seismic transients should have little impact on faults if the duration of the transient is smaller than the timescale for nucleation of slip. We reexamine the dynamics of stress triggering during stick‐slip sliding on a laboratory fault and make three important observations that pertain to earthquake triggering. (1) Delayed triggering (clock advance) occurs for both bare granite surfaces and granular gouge prior to the onset of instantaneous triggering. (2) Triggering occurs much earlier in the stick‐slip cycle than expected for a simple Coulomb stress threshold. (3) Shorter‐period (higher stressing rate) pulses are more effective at triggering than longer‐period pulses of the same stress amplitude. We use numerical simulations to show that rate‐state friction can explain each of the observed features but not all three simultaneously. Only the Ruina slip law for state evolution, in which faults must slip to heal, can reproduce early‐onset and stressing rate‐dependent triggering. The laboratory and numerical experiments show that faults can remain relatively weak over much of the seismic cycle and that the triggered response depends on a competition between healing and weakening during triggered slip. Transient stressing at seismic frequencies may be more effective at triggering earthquakes than previously recognized.

Modulation of elementary calcium release mediates a transition from puffs to waves in an IP3R cluster model.

The oscillating concentration of intracellular calcium is one of the most important examples for collective dynamics in cell biology. Localized releases of calcium through clusters of inositol 1,4,5-trisphosphate receptor channels constitute elementary signals called calcium puffs. Coupling by diffusing calcium leads to global releases and waves, but the exact mechanism of inter-cluster coupling and triggering of waves is unknown. To elucidate the relation of puffs and waves, we here model a cluster of IP3R channels using a gating scheme with variable non-equilibrium IP3 binding. Hybrid stochastic and deterministic simulations show that puffs are not stereotyped events of constant duration but are sensitive to stimulation strength and residual calcium. For increasing IP3 concentration, the release events become modulated at a timescale of minutes, with repetitive wave-like releases interspersed with several puffs. This modulation is consistent with experimental observations we present, including refractoriness and increase of puff frequency during the inter-wave interval. Our results suggest that waves are established by a random but time-modulated appearance of sustained release events, which have a high potential to trigger and synchronize activity throughout the cell.

Triggering waves in nonlinear lattices: Quest for anharmonic phonons and corresponding mean-free paths

Guided by a stylized experiment we develop a self-consistent anharmonic phonon concept for nonlinear lattices which allows for explicit ``visualization.'' The idea uses a small external driving force which excites the front particles in a nonlinear lattice slab and subsequently one monitors the excited wave evolution using molecular dynamics simulations. This allows for a simultaneous, direct determination of the existence of the phonon mean-free path with its corresponding anharmonic phonon wave number as a function of temperature. The concept for the mean-free path is very distinct from known prior approaches: the latter evaluate the mean-free path only indirectly, via using both a scale for for the phonon relaxation time and yet another one for the phonon velocity. Notably, the concept here is neither limited to small lattice nonlinearities nor to small frequencies. The scheme is tested for three strongly nonlinear lattices of timely current interest which either exhibit normal or anomalous heat transport.

Surface acoustic wave triggering of giant magnetocaloric effect in MnAs/GaAs devices

We have measured the attenuation of surface acoustic waves travelling through lithographied hybrid structures composed of MnAs thin films epitaxied on piezoelectric GaAs. Around room temperature, MnAs presents a well-known magnetostructural phase transition accompanied by a giant magnetocaloric effect. A large temperature dependent thermoelastic attenuation is found despite the film is much thinner (100 nm) than the wave penetration depth (∼10 μm). This phenomenon is attributed to strain-induced triggering of the MnAs magneto-caloric effect. We find that the frequency (ν) dependence of attenuation is quite unusual, ∼ν1.7, and that the attenuation weakly depends on the film thickness. We show that this behavior is due to the peculiar thermal boundary conditions imposed by magneto-caloric MnAs to the overall device.

Identification of the propagation mode of a solar wind wave associated with Pc5 pulsations in the magnetosphere

Abstract. A case study of a magnetohydrodynamic (MHD) wave in the solar wind that is strongly correlated with a magnetospheric field line resonance observed by the SuperDARN (Super Dual Auroral Radar Network) radar at Sanae, Antarctica is presented. The data from the ACE (Advanced Composition Explorer) satellite at the solar libration point are analysed. The data time series are bandpass filtered at the pulsation frequency and the analytic signal deduced. From these data the partition of energy between the field components is computed. It is shown that energy is equally partitioned between the kinetic energy and transverse magnetic potential energy densities. The energy flux vector is closely aligned with the background magnetic field. The transverse magnetic and velocity components are in antiphase. This is the first identification of the triggering wave as a transverse Alfvén wave which originates upstream from the space craft and is propagated to the magnetosphere to trigger the pulsation.

A re-evaluation of dust processing in supernova shock waves

Context. There is a long-standing and large discrepancy between the timescale for dust formation around evolved stars and the rapid dust destruction timescale in interstellar shocks. Aims. We use our latest estimates for dust processing to re-evaluate the dust destruction efficiency in supernova triggered shock waves, estimate the dust lifetime, and calculate the emission and extinction from shocked dust. Methods. We modelled the sputtering and fragmentation of grains in interstellar shocks for shock velocities between 50 km s −1 and 200 km s −1 . We constrained the dust destruction using our recent dust model. Finally, we coupled our code to the DustEM code in order to estimate the emission and extinction from the dust post-shock. Results. Carbonaceous grains are quickly destroyed, even in a 50 km s −1 shock, leading to a shorter lifetime than in previous studies. Silicate grains appear to be more resilient, but the new destruction lifetime that we find is similar to previous studies and short compared to the dust injection timescale. Conclusions. The calculated fraction of elements locked in grains is not compatible with the observed values and therefore implies the re-formation of dust in the dense regions of the interstellar medium. Better modelling of the silicate sputtering together with hydrodynamical simulations of interstellar shocks, appears to reduce the silicate destruction and may close the destruction-formation timescale gap.

Interactions of energetic electrons with ULF waves triggered by interplanetary shock: Van Allen Probes observations in the magnetotail

AbstractWe present in situ observations of a shock‐induced substorm‐like event on 13 April 2013 observed by the newly launched Van Allen twin probes. Substorm‐like electron injections with energy of 30–500 keV were observed in the region from L∼5.2 to 5.5 immediately after the shock arrival (followed by energetic electron drift echoes). Meanwhile, the electron flux was clearly and strongly varying on the ULF wave time scale. It is found that both toroidal and poloidal mode ULF waves with a period of 150 s emerged following the magnetotail magnetic field reconfiguration after the interplanetary (IP) shock passage. The poloidal mode is more intense than the toroidal mode. The 90° phase shift between the poloidal mode Br and Ea suggests the standing poloidal waves in the Northern Hemisphere. Furthermore, the energetic electron flux modulations indicate that the azimuthal wave number is ∼14. Direct evidence of drift resonance between the injected electrons and the excited poloidal ULF wave has been obtained. The resonant energy is estimated to be between 150 keV and 230 keV. Two possible scenaria on ULF wave triggering are discussed: vortex‐like flow structure‐driven field line resonance and ULF wave growth through drift resonance. It is found that the IP shock may trigger intense ULF wave and energetic electron behavior at L∼3 to 6 on the nightside, while the time profile of the wave is different from dayside cases.

TRIGGERING COLLAPSE OF THE PRESOLAR DENSE CLOUD CORE AND INJECTING SHORT-LIVED RADIOISOTOPES WITH A SHOCK WAVE. III. ROTATING THREE-DIMENSIONAL CLOUD CORES

A key test of the supernova triggering and injection hypothesis for the origin of the solar system's short-lived radioisotopes is to reproduce the inferred initial abundances of these isotopes. We present here the most detailed models to date of the shock wave triggering and injection process, where shock waves with varied properties strike fully three dimensional, rotating, dense cloud cores. The models are calculated with the FLASH adaptive mesh hydrodynamics code. Three different outcomes can result: triggered collapse leading to fragmentation into a multiple protostar system; triggered collapse leading to a single protostar embedded in a protostellar disk; or failure to undergo dynamic collapse. Shock wave material is injected into the collapsing clouds through Rayleigh-Taylor fingers, resulting in initially inhomogeneous distributions in the protostars and protostellar disks. Cloud rotation about an axis aligned with the shock propagation direction does not increase the injection efficiency appreciably, as the shock parameters were chosen to be optimal for injection even in the absence of rotation. For a shock wave from a core-collapse supernova, the dilution factors for supernova material are in the range of $\sim 10^{-4}$ to $\sim 3 \times 10^{-4}$, in agreement with recent laboratory estimates of the required amount of dilution for $^{60}$Fe and $^{26}$Al. We conclude that a type II supernova remains as a promising candidate for synthesizing the solar system's short-lived radioisotopes shortly before their injection into the presolar cloud core by the supernova's remnant shock wave.

Role of the Vision Van, a mobile ophthalmic outpatient clinic, in the Great East Japan Earthquake.

PurposeThe Great East Japan Earthquake of March 11, 2011 triggered powerful tsunami waves off the northeastern Pacific coast of Japan that destroyed almost all of the built-up areas along the coast. The study reported here examined the role played by the Vision Van, a mobile outpatient ophthalmological clinic, in providing eye care to disaster evacuees.MethodsThis was a retrospective case-series study of 2,070 victims (male: 732, female: 1,338) who visited the Vision Van. The subjects’ medical records were examined retrospectively and analyzed in terms of age, sex, and date of visit to the Vision Van. Information regarding each patient’s chief complaint, diagnosis, medication(s) prescribed, and eyeglasses and contact lenses provided, was also examined.ResultsThe Vision Van was used to conduct medical examinations on 39 days between April 23 and June 29, 2011. The average number of subjects visiting the Vision Van each day was 53±31 (range: 7–135), with examinations carried out in Miyagi Prefecture and Iwate Prefecture. The most frequent complaint was a need for eye drops (871/2,070 [42.1%]). The second and third most frequent complaints, respectively, were the need for contact lenses (294/2,070 [14.2%]) and eyeglasses (280/2,070 [13.5%]). The most frequent ocular disease diagnosis was cataract (497/2,070 [24.0%]). Eye drops were prescribed to 74.1% of the subjects.ConclusionMobile clinics such as the Vision Van provide valuable care, in this case, particularly to individuals who lost or left behind eyeglasses or contact lenses while escaping a natural disaster, and to subjects with chronic eye disease.

Tremor Sweet Spots

Geophysics![Figure][1] CREDIT: © WIEDE, U. & M./ARCO IMAGES GMBH/ALAMY Seismic tremor is thought to be indicative of the slow release of small amounts of stress along plate boundaries, but it can also be triggered by large-amplitude seismic waves generated during large earthquakes. Gomberg and Prejean determined the distribution of tremor in Alaska after 11 of the largest earthquakes ( M < 7.2) around the globe between 2006 and 2012. As in previous observations, triggered tremor in the Aleutian Islands is related to the transition of friction along the subducting plate boundary from a locked state to a creeping state. However, tremor was also triggered in central mainland Alaska—a region far away from the subduction zone and devoid of any major crustal faults or appreciable seismic activity. Because there was no single characteristic of the triggering wave source or tectonic environment associated with the two regions, transient frictional processes at the plate interface may be responsible for tremor triggering. However, according to GPS data, neither zone shows any clear evidence of other concurrent related seismic processes such as slow slip events. J. Geophys. Res. 118 , 10.1002/2013JB010273 (2013). [1]: pending:yes

A proposed baroclinic wave test case for deep‐ and shallow‐atmosphere dynamical cores

AbstractIdealised studies of key dynamical features of the atmosphere provide insight into the behaviour of atmospheric models. A very important, well understood, aspect of midlatitude dynamics is baroclinic instability. This can be idealised by perturbing a vertically sheared basic state in geostrophic and hydrostatic balance. An unstable wave mode then results with exponential growth (due to linear dynamics) in time until, eventually, nonlinear effects dominate and the wave breaks.A new, unified, idealised baroclinic instability test case is proposed. This improves on previous ones in three ways. First, it is suitable for both deep‐ and shallow‐atmosphere models. Second, the constant surface pressure and zero surface geopotential of the basic state makes it particularly well‐suited for models employing a pressure‐ or height‐based vertical coordinate. Third, the wave triggering mechanism selectively perturbs the rotational component of the flow; this, together with a vertical tapering, significantly improves dynamic balance.

Triggered tremor sweet spots in Alaska

To better understand what controls fault slip along plate boundaries, we have exploited the abundance of seismic and geodetic data available from the richly varied tectonic environments composing Alaska. A search for tremor triggered by 11 large earthquakes throughout all of seismically monitored Alaska reveals two tremor “sweet spots”—regions where large‐amplitude seismic waves repeatedly triggered tremor between 2006 and 2012. The two sweet spots locate in very different tectonic environments—one just trenchward and between the Aleutian islands of Unalaska and Akutan and the other in central mainland Alaska. The Unalaska/Akutan spot corroborates previous evidence that the region is ripe for tremor, perhaps because it is located where plate‐interface frictional properties transition between stick‐slip and stably sliding in both the dip direction and laterally. The mainland sweet spot coincides with a region of complex and uncertain plate interactions, and where no slow slip events or major crustal faults have been noted previously. Analyses showed that larger triggering wave amplitudes, and perhaps lower frequencies (&lt;~0.03 Hz), may enhance the probability of triggering tremor. However, neither the maximum amplitude in the time domain or in a particular frequency band, nor the geometric relationship of the wavefield to the tremor source faults alone ensures a high probability of triggering. Triggered tremor at the two sweet spots also does not occur during slow slip events visually detectable in GPS data, although slow slip below the detection threshold may have facilitated tremor triggering.

Triggering process of electromagnetic ion cyclotron rising tone emissions in the inner magnetosphere

Spacecraft observations and simulations show generation of coherent electromagnetic ion cyclotron (EMIC) triggered emissions with rising tone frequencies. In the inner magnetosphere, the spontaneously triggered EMIC waves are generated by the energetic protons with large temperature anisotropy. We reproduced EMIC triggered emissions in the Earth's magnetosphere by real scale hybrid simulations with cylindrical magnetic geometry. We obtained spontaneously triggered nonlinear EMIC waves with rising frequencies in the H+band of the EMIC dispersion relation. The proton holes in the phase space are formed. We have also derived the theoretical optimum wave amplitude for triggering process of the EMIC nonlinear wave growth. The optimum wave amplitude and the nonlinear transition time show a good agreement with the present simulation result. The nonlinear wave growth over a limited time forms a subpacket structure of a rising tone emission. The formation process of a subpacket is repeated because of a new triggering wave generated by the phase‐organized protons, which are released from the previous subpacket. Then, the EMIC triggered emission is formed as a train of subpackets generated at different rising frequencies.

The Great East Japan Earthquake: Lessons Learned at Tohoku University Hospital During the First 72 Hours

A 9.0-magnitude earthquake occurred off the northeast coast of Japan at 2:46 p.m. (local time) on Friday, 11 March 2011, with the epicenter approximately 70 km (43 mi) east of the Oshika Peninsula and the hypocenter at a depth of approximately 32 km (20 mi) below sea level [Figure 1(a)] [1]. The earthquake triggered powerful tsunami waves, which reached heights of up to 40.5 m (133 ft) in Miyako and traveled around 4 km (about 2.5 mi) inland in the Sendai area. As of 30 March 2012, a total of 18,897 people were either dead or missing.

A Global Search for Triggered Tremor Following the 2011 Mw 9.0 Tohoku Earthquake

Abstract The 2011 M w 9.0 Tohoku, Japan, earthquake triggered deep tectonic tremor and shallow microearthquakes in numerous places worldwide. Here, we conduct a systematic survey of triggered tremor in regions where ambient or triggered tremor has been previously identified. Tremor was triggered in the following regions: south‐central Alaska, the Aleutian Arc, Shikoku in southwest Japan, the North Island of New Zealand, southern Oregon, the Parkfield–Cholame section of the San Andreas fault in central California, the San Jacinto fault in southern California, Taiwan, and Vancouver Island. We find no evidence of triggered tremor in the Calaveras fault in northern California. One of the most important factors in controlling the triggering potential is the amplitude of the surface waves. Data examined in this study suggest that the threshold amplitude for triggering tremor is ∼0.1 cm/s, which is equivalent to a dynamic stress threshold of ∼10 kilopascals. The incidence angles of the teleseismic surface waves also affect the triggering potentials of Love and Rayleigh waves. The results of this study confirm that both Love and Rayleigh waves contribute to triggering tremor in many regions. In regions where both ambient and triggered tremor are known to occur, tremor triggered by the Tohoku event generally occurred at similar locations with previously identified ambient and/or triggered tremor, further supporting the notion that although the driving forces of triggered and ambient tremor differ, they share similar mechanisms. We find a positive relationship between the amplitudes of the triggering waves and those of the triggered tremor, which is consistent with the prediction of the clock‐advance model. Online Material: Table of measured parameters and other information related to triggering/nontriggering information, and figures of observed seismograms.

Frequency of Triggered Ca2+ Waves is Increased in Atrial Myocytes during Heart Failure

Triggered Ca2+ waves develop during rapid pacing in atrial myocytes and are therefore likely to contribute to action potential (AP) duration, thus establishing repolarization gradients and causing reentry. The goal of this study was to investigate how Ca2+ wave properties are altered in heart failure (HF). Myocytes were isolated from the left atrium of dogs paced rapidly for 5-6 weeks and Ca2+ cycling was studied during rapid pacing using rhod-2AM and confocal microscopy (37oC). In control myocytes, the incidence of triggered Ca2+ waves increased with pacing rate and this frequency dependence was shifted to slower rates in HF myocytes. The increase in wave frequency was directly related to the increase in diastolic [Ca2+] with increasing rate, which was exaggerated in HF myocytes. Propagation velocity and distance (percent of cell length) also decreased in HF and there was a shift in the distribution of propagation distance to more short waves and fewer long waves. A low concentration of caffeine (0.5mM, to increase RyR Ca2+ sensitivity) abolished triggered waves and restored normal Ca2+ transients even at high pacing rates. We conclude that 1) triggered Ca2+ wave frequency is increased in HF despite decreased propagation distance and velocity, 2) wave incidence in HF may be related to a greater sensitivity to the rate-induced rise in diastolic [Ca2+], and 3) the fact that low [caffeine] abolished waves and restored normal Ca2+ transients, suggests that triggered waves occur as a result of a reduced sensitivity of SR Ca2+ release to trigger Ca2+ influx. This form of aberrant Ca2+ cycling during the AP may affect the beat-to-beat regulation of AP duration, which may contribute to establishing the substrate for reentrant arrhythmias by formation of repolarization gradients, especially in the setting of HF.

Detection of seismic events triggered by P-waves from the 2011 Tohoku-Oki earthquake

Large-amplitude surface waves from the 2011 Tohoku-Oki earthquake triggered many seismic events across Japan, while the smaller amplitude P-wave triggering remains unclear. A spectral method was used to detect seismic events triggered by the first arriving P-waves over Japan. This method uses a reference event to correct for source and propagation effects, so that the local response near the station can be examined in detail. P-wave triggering was found in the regions where triggered non-volcanic tremor (NVT) has been observed, and some seismic and volcanic regions. The triggering strain due to P-waves is of the order of 10−8 to 10−7, which is 1 to 2 orders of magnitude smaller than the triggering strain necessary for the surface wave triggering. In the regions of NVT, the triggered event was not identified with slow events, but with other seismic events such as tectonic earthquakes. The sequence of triggering in the regions started with P-wave arrivals. The subsequent surface waves contributed to triggering of NVT, possibly together with slow slip, which resulted in the large amplitude of the NVT.

THE 2011 GREAT EAST JAPAN EARTHQUAKE: A REPORT OF A REGIONAL HOSPITAL IN FUKUSHIMA PREFECTURE COPING WITH THE FUKUSHIMA NUCLEAR DISASTER

A catastrophic undersea megathrust earthquake of magnitude 9.0 off the coast of Japan occurred at 14:46 JST on Friday, 11 March 2011. The earthquake triggered powerful tsunami waves, and the tsunami precipitated Fukushima nuclear accidents. After the terrible earthquake, many people fled from the nuclear accident and arrived at places far from the nuclear power plant. In this article, I present a story of one measure devised to deal with the problem of the Fukushima nuclear accident at a regional hospital of Fukushima prefecture, Aizu General Hospital, which is located far from the Fukushima nuclear plant. In addition, I briefly report the current situation of Fukushima prefecture after the 2011 Great East Japan earthquake. In our hospital, the countermeasure headquarters was established to supply medical care for those who had been injured by tsunami waves and the Fukushima nuclear accident. Especially, the screening for radioactive exposure using a dosimeter to take decontamination measures for cases of external exposure was extremely important task. Nevertheless, because the accurate knowledge related to radioactive contamination didn't provide, most medical staff fell into confusion. Fukushima prefecture has been 'shrinking' since the nuclear accident. However, today, although some hot spots remain in residential areas, the radioactive contamination is decreasing little by little. Many people in Fukushima Prefecture advance as one, facing forward. Recently, decontamination projects started. Efforts must be continued over a long period.

Particle simulations of whistler‐mode rising‐tone emissions triggered by waves with different amplitudes

We perform self‐consistent electromagnetic particle simulations to analyze whistler‐mode triggered emissions in the magnetosphere. The whistler‐mode triggering waves with different wave amplitudes and a constant frequency are injected at the equator. With triggering wave amplitudes greater than the threshold for the nonlinear wave growth, rising‐tone emissions are successfully excited near the equator. The detailed time evolutions of amplitudes and frequencies of the rising‐tone emissions show similar development. A recent theoretical study found the optimum amplitude of triggering waves for rising‐tone emissions. The optimum amplitude condition is confirmed by the simulations. A triggering wave with an amplitude much greater than the optimum amplitude cannot trigger a rising emission. In a process where triggered emissions develop, phase‐organized resonant electrons clearly appear in the velocity‐phase space, contributing to the nonlinear wave growth. The simulation study shows that amplitudes and frequency sweep rates of triggered emissions do not depend on the amplitude of a triggering wave.

Coastal and Estuarine Morphology Changes Induced by the 2011 Great East Japan Earthquake Tsunami

The 2011 Great East Japan Earthquake that occurred on March 11, 2011, had magnitude of 9.0 on the Richter Scale with the epicenter approximately 70 km east of the Oshika Peninsula in Miyagi Prefecture. This earthquake triggered terrible tsunami waves which hit the coast of Japan and propagated around the Pacific Ocean. The earthquake and tsunami caused extensive and severe infrastructural damage, such as damages of coastal protection structures and buildings, and significantly changed coastal and river morphology. This paper presents tsunami-induced coastal and estuarine morphology changes in Miyagi Prefecture, Japan, and subsequent recovery process in each study area. On sandy coasts, discontinuous coastal protection is likely to be severely damaged, resulting in serious erosion in the surrounding sandy coast. Furthermore, severe breaching was observed on sandy coasts where formerly river mouth was located, due to strong return flow from the catchment area. The restoration process of the coast and estuaries is highly dependent on sediment supply availability in the surrounding area.