Dynamic Stress Changes Research Articles

Intraplate earthquake swarms in West Bohemia/Vogtland (Central Europe)

West Bohemia (Czech Republic) and Vogtland (Germany) are among the most active intraplate earthquake-swarm areas in Europe with the largest events mostly of magnitudes $M_L$ \< 4.0. The principal char-acteristics of the West Bohemia/Vogtland earthquake swarms are derived on the basis of local observations from the network WEBNET during the period between 1991 and 2009. Swarm microearthquakes clustered in number of small focal areas; however, about 90\% of the total seismic moment was released in the Nový Kostel (NK) focal zone, which was formed by an NNW striking and steeply dipping fault plane. The focal depths ranged between 5 and 22 km in the whole region and between 4.5 and 11 km in the NK zone, while most of the swarm events clustered at depths from 8.5 to 9.5 km. All larger earthquake swarms took place in the NK zone; though they were located close, they differed significantly in their evolution. Two swarms, the 2000 ($M_L$ ≤ 3.3) and 2008 ($M_L$ ≤ 3.8) swarms were located on the same portion of the NK focal zone which implies reactivation of the same fault segment. Attention was paid to source mechanisms of the 1997 and 2000 swarms, particularly to the non-shear components in the 1997-swarm earthquakes. All the 1997 sources were of dipole character: the slightly compressive dipoles dominating in the first swarm phase were replaced by tensile dipoles in the second phase. On the contrary, the 2000 swarm events possessed pure double-couple sources which resulted in pure shears along the NK fault. We infer that the pure-shear rupturing in the 2000 swarm was on account of the favourably oriented NK fault plane with respect to the local tectonic stress field whereas the additional tensile forces were needed for rupturing due to the unfavourably oriented 1997-swarm fault segments. Further, we analyzed statistic characteristics and we show that the magnitude-frequency distribution with the b-value ≈ 1.0 is typical for the West Bohemia/Vogtland earthquake swarms and that scalar moments $M_0$ and the WEBNET magnitudes $M_L$ are related according to power-law $M_0$ ∝ 10$^{M_L}$, which is inconsistent with the definition of the moment magnitude $M_0$ ∝ 10$^{1.5 M_w}$ given by Kanamori (1977). We also show that this inconsistency results in a discrepancy in b-value of the magnitude-frequency distribution. Taking into account total seismic moment of the 2000 and 2008 swarms we infer that $M_{L_{MAX}}$ ∼ 5.0 to 5.3 is the maximum expected magnitude in the main NK focal zone and thus in the whole region. There is still an open question concerning the internal and external triggering of the West Bohemia/Vogtland earthquake swarms. We refer to the results of our recent study and infer that the earthquake swarm probably represents gradually propagating rupture along the fault and that both static and dynamic Coulomb stress changes along the fault plane due to co-seismic slip contribute significantly to triggering of the swarm events. Repeatedly observed almost simultaneous occurrence of seismic activity in different focal zones suggests that common triggering forces act in a broader area of West Bohemia/Vogtland.

The 2009 Samoa–Tonga great earthquake triggered doublet

Great earthquakes (having seismic magnitudes of at least 8) usually involve abrupt sliding of rock masses at a boundary between tectonic plates. Such interplate ruptures produce dynamic and static stress changes that can activate nearby intraplate aftershocks, as is commonly observed in the trench-slope region seaward of a great subduction zone thrust event. The earthquake sequence addressed here involves a rare instance in which a great trench-slope intraplate earthquake triggered extensive interplate faulting, reversing the typical pattern and broadly expanding the seismic and tsunami hazard. On 29 September 2009, within two minutes of the initiation of a normal faulting event with moment magnitude 8.1 in the outer trench-slope at the northern end of the Tonga subduction zone, two major interplate underthrusting subevents (both with moment magnitude 7.8), with total moment equal to a second great earthquake of moment magnitude 8.0, ruptured the nearby subduction zone megathrust. The collective faulting produced tsunami waves with localized regions of about 12 metres run-up that claimed 192 lives in Samoa, American Samoa and Tonga. Overlap of the seismic signals obscured the fact that distinct faults separated by more than 50 km had ruptured with different geometries, with the triggered thrust faulting only being revealed by detailed seismic wave analyses. Extensive interplate and intraplate aftershock activity was activated over a large region of the northern Tonga subduction zone.

Stress interactions of three moderate size earthquakes in Afyon, southwestern Turkey

We analyze three moderate size earthquakes occurred in the Afyon region of southwestern Turkey on December 15, 2000 ( M w = 6.0) and February 3, 2002 ( M w = 6.5 and M w = 5.8). This earthquake sequence took place on the Sultandağ Fault having dominantly normal faulting mechanisms with different orientations in an extensional tectonic regime. We relocate these mainshocks and their large aftershocks and use the waveform data to determine the rupture dimensions and directivities. We carry out both static and dynamic stress analysis to investigate stress interactions and possible earthquake triggering mechanisms in this sequence. We show that the 2002, M w = 6.5 rupture started at the termination of the 2000, M w = 6.0 earthquake, where the calculated Coulomb stress changes increased more than 0.5 bar. Thus, we conclude that the coseismic stress increase by the 2000 event favored the nucleation and promoted the timing of the 2002 event. An intense seismic activity, identified as the Kızıldağ aftershock zone, developed following both of the large mainshocks where the third largest earthquake ( M w = 5.8) of the sequence occurred 2 h after the 2002, M w = 6.5 mainshock. The Coulomb stress calculations of the 2000 earthquake shows no influence in this zone while the static Coulomb stress changes due to the 2002, M w = 6.5 mainshock raised the Coulomb stresses an additional 0.3–0.7 bar in the Kızıldağ aftershock zone. Thus, we infer that such changes in the Coulomb stresses positively influence the occurrence of the aftershocks in this zone. Since the Kızıldağ aftershock zone takes place in a geothermal area, we compute dynamic stress changes imposed by the 2000 and 2002 mainshocks. The computed peak dynamic stress levels for both mainshocks are found much higher than the static stress changes calculated within the Kızıldağ aftershock zone. Thus, we propose that transient stress triggering, most likely involving elevated fluid pressures in the hydrothermal systems present in this region, may have played a major role in the initiation of increased seismicity followed by local, multiple elastic stress triggering leading to the further development of aftershocks and the occurrence of the M w = 5.8 mainshock.

On near‐source earthquake triggering

When one earthquake triggers others nearby, what connects them? Two processes are observed: static stress change from fault offset and dynamic stress changes from passing seismic waves. In the near‐source region (r ≤ 50 km for M ∼ 5 sources) both processes may be operating, and since both mechanisms are expected to raise earthquake rates, it is difficult to isolate them. We thus compare explosions with earthquakes because only earthquakes cause significant static stress changes. We find that large explosions at the Nevada Test Site do not trigger earthquakes at rates comparable to similar magnitude earthquakes. Surface waves are associated with regional and long‐range dynamic triggering, but we note that surface waves with low enough frequency to penetrate to depths where most aftershocks of the 1992 M = 5.7 Little Skull Mountain main shock occurred (∼12 km) would not have developed significant amplitude within a 50‐km radius. We therefore focus on the best candidate phases to cause local dynamic triggering, direct waves that pass through observed near‐source aftershock clusters. We examine these phases, which arrived at the nearest (200–270 km) broadband station before the surface wave train and could thus be isolated for study. Direct comparison of spectral amplitudes of presurface wave arrivals shows that M ∼ 5 explosions and earthquakes deliver the same peak dynamic stresses into the near‐source crust. We conclude that a static stress change model can readily explain observed aftershock patterns, whereas it is difficult to attribute near‐source triggering to a dynamic process because of the dearth of aftershocks near large explosions.

Magnetorheology of soft magnetic carbonyl iron suspension with single-walled carbon nanotube additive and its yield stress scaling function

The serious dispersion problem of carbonyl iron (CI) based magnetorheological (MR) fluid, due to the large density mismatch between CI particles and continuous medium, has hampered its MR applications. To resolve this undesirable sedimentation, we introduced fibrous single-walled carbon nanotube (SWNT) into CI suspension as additives. The dynamic yield stress change measured as a function of magnetic field strength was examined by adopting a universal equation which was originally applied for electrorheological (ER) fluids. In addition, the viscoelastic performances of CI/SWNT suspension were compared to investigate the influence of additives on the pristine CI suspension. The sedimentation ratio was also examined to confirm the role of submicron SWNT bundles.

Seismicity Rate Changes along the Central California Coast due to Stress Changes from the 2003 M 6.5 San Simeon and 2004 M 6.0 Parkfield Earthquakes

Abstract We investigated the relationship between seismicity rate changes and modeled Coulomb static stress changes from the 2003 M 6.5 San Simeon and the 2004 M 6.0 Parkfield earthquakes in central California. Coulomb stress modeling indicates that the San Simeon mainshock loaded parts of the Rinconada, Hosgri, and San Andreas strike-slip faults, along with the reverse faults of the southern Los Osos domain. All of these loaded faults, except for the San Andreas, experienced a seismicity rate increase at the time of the San Simeon mainshock. The Parkfield earthquake occurred 9 months later on the loaded portion of the San Andreas fault. The Parkfield earthquake unloaded the Hosgri fault and the reverse faults of the southern Los Osos domain, which both experienced seismicity rate decreases at the time of the Parkfield event, although the decreases may be related to the decay of San Simeon-triggered seismicity. Coulomb stress unloading from the Parkfield earthquake appears to have altered the aftershock decay rate of the southern cluster of San Simeon aftershocks, which is deficient compared to the expected number of aftershocks from the Omori decay parameters based on the pre-Parkfield aftershocks. Dynamic stress changes cannot explain the deficiency of aftershocks, providing evidence that static stress changes affect earthquake occurrence. However, a burst of seismicity following the Parkfield earthquake at Ragged Point, where the static stress was decreased, provides evidence for dynamic stress triggering. It therefore appears that both Coulomb static stress changes and dynamic stress changes affect the seismicity rate.

The 1911 M 6.6 Calaveras Earthquake: Source Parameters and the Role of Static, Viscoelastic, and Dynamic Coulomb Stress Changes Imparted by the 1906 San Francisco Earthquake

The occurrence of a right-lateral strike-slip earthquake in 1911 is inconsistent with the calculated ![Graphic][1] static stress decrease imparted by the 1906 rupture at that location on the Calaveras fault, and 5 yr of calculated post-1906 viscoelastic rebound does little to reload the fault. We have used all available first-motion, body-wave, and surface-wave data to explore possible focal mechanisms for the 1911 earthquake. We find that the event was most likely a right-lateral strike-slip event on the Calaveras fault, larger than, but otherwise resembling, the 1984 M w 6.1 Morgan Hill earthquake in roughly the same location. Unfortunately, we could recover no unambiguous surface fault offset or geodetic strain data to corroborate the seismic analysis despite an exhaustive archival search. We calculated the static and dynamic Coulomb stress changes for three 1906 source models to understand stress transfer to the 1911 site. In contrast to the static stress shadow, the peak dynamic Coulomb stress imparted by the 1906 rupture promoted failure at the site of the 1911 earthquake by 1.4–5.8 bar. Perhaps because the sample is small and the aftershocks are poorly located, we find no correlation of 1906 aftershock frequency or magnitude with the peak dynamic stress, although all aftershocks sustained a calculated dynamic stress of ≥3 bar. Just 20 km to the south of the 1911 epicenter, we find that surface creep of the Calaveras fault at Hollister paused for ∼17 yr after 1906, about the expected delay for the calculated static stress drop imparted by the 1906 earthquake when San Andreas fault postseismic creep and viscoelastic relaxation are included. Thus, the 1911 earthquake may have been promoted by the transient dynamic stresses, while Calaveras fault creep 20 km to the south appears to have been inhibited by the static stress changes. [1]: /embed/inline-graphic-1.gif

A global search for stress shadows

Debate continues regarding the relative proportion of earthquakes triggered by passing seismic waves versus static stress changes from a main shock. Static stress changes are expected to have long‐term effects on earthquake probabilities, whereas dynamic stress changes due to the passing of seismic waves should not. Both mechanisms are expected to raise seismicity rates in some areas, but only static stress change calculations predict rate decrease shadows. Thus, identification of post‐main‐shock earthquake suppression is diagnostic of a static stress change process. We note that in principle, static stress change theory predicts suppression of particular earthquake mechanisms in a shadow zone rather than an overall rate reduction. A stress shadow can therefore be characterized by a change in the average earthquake focal mechanism before and after a main shock that results from suppression of a given mechanism type. We examined average mechanisms from ±2° radii and 5‐year periods before and after 119 Ms ≥ 7 main shock earthquakes drawn from the Harvard Centroid Moment Tensor (CMT) catalog. Significant average mechanism changes caused by earthquake suppression were found in only two cases. However, by stacking the data, we were able to resolve statistically significant suppression of particular post‐main‐shock focal mechanisms. This indicates that, while static stress shadows are subtle, they are indeed present in the global catalog.

Motion on upper‐plate faults during subduction zone earthquakes: Case of the Atacama Fault System, northern Chile

Motion on the Atacama Fault System (AFS) in northern Chile is driven by Andean subduction zone processes. We use two approaches, observational and theoretical, to evaluate how the AFS and other forearc faults responded to coseismic stress induced by one well‐studied megathrust earthquake, the 1995 Mw = 8.1 Antofagasta event. We use synthetic aperture radar interferometry (InSAR) to search for small‐scale coseismic and postseismic deformation on individual faults. The InSAR data are ambiguous: some images show offset consistent with coseismic faulting on the Paposo segment of the AFS and others lack such signal. The fact that we do not observe the fault‐like displacement in all coseismic interferograms suggests that atmospheric contamination, not tectonic deformation, is responsible for the signal. To explore the capacity of the earthquake to trigger motion on upper plate faults, we use seven published slip maps constrained by geodetic and/or seismic data to calculate static and dynamic Coulomb stress change (CSC) on faults in the Antofagasta region. The static CSC field varies between models and depends on the distribution of coseismic interplate slip. On the basis of the CSC distribution predicted by our preferred model constrained by all available data, we suggest it was unlikely that the Antofagasta earthquake directly triggered normal motion on the AFS, and the InSAR data are consistent with this null result. Field reports of normal faulting related to the earthquake may reflect recent (but not coseismic) motion or highly localized behavior not representative of the regional coseismic stress field.

Numerical simulation of dynamic Coulomb stress changes induced by M6.5 earthquake in Wuding, Yunnan and its relationship with aftershocks

Based on the discrete wavenumber method, we calculate the fields of dynamic Coulomb rupture stress changes and static stress changes caused by M6.5 earthquake in Wuding, and study their relationship with the subsequent aftershocks. The results show that the spatial distribution patterns of the positive region of dynamic stress peak value and static stress peak value are similarly asymmetric, which are basically identical with distribution features of aftershock. The dynamic stress peak value and the static stress in the positive region are more than 0.1 MPa and 0.01 MPa of the triggering threshold, respectively, which indicates that the dynamic and static stresses are helpful for the occurrence of aftershock. This suggests that both influences of dynamic and static stresses should be considered other than only either of them when studying aftershock triggering in near field.

Triggering of the Lusi mud eruption: Earthquake versus drilling initiation

ABSTRACTThe Lusi mud volcano in East Java has erupted unabated for almost 2 yr, fl ooding an area of 7 km 2 and displacing more than 25,000 people. Despite its disastrous impact, the mechanism for triggering the Lusi eruption remains highly controversial; two distinct mechanisms have been proposed. One hypothesis suggests that the eruption was triggered by the M w 6.3 earth-quake that struck Yogyakarta (250 km from Lusi) two days before the eruption. However, an examination of static and dynamic stress changes and stress transfer mechanisms indicates that the Yogyakarta earthquake was at least an order of magnitude too small to reactivate faults and open fl uid fl ow pathways under Lusi. An alternate theory suggests that Lusi was triggered by a blowout following drilling problems in the nearby Banjar Panji-1 well. Blowouts result from an inability to control pore fl uid intakes into the borehole and typically occur when the drilling win-dow (fracture pressure minus pore pressure) is approximately zero and when there is insuffi cient protective casing of the well bore. Pore and fracture pressure data from Banjar Panji-1 indicate that the well had a narrow drilling window of only 0–2.3 MPa. Furthermore, two planned casing points were skipped during drilling, resulting in 1742 m of unprotected borehole. The combina-tion of hazardously narrow drilling window and long uncased borehole would have made drill-ing problems in Banjar Panji-1 diffi cult to control, placing the well at high risk of blowing out. Furthermore, well-bore pressures following drilling problems in Banjar Panji-1 reached magni-tudes in excess of the fracture pressure and thus were suffi cient to create fl uid fl ow pathways in the subsurface. Therefore, we suggest that no viable method is known by which the Yogyakarta earthquake could have triggered the mudfl ow and that a blowout in the Banjar Panji-1 well was the most likely mechanism for triggering the Lusi eruption.Keywords:

Triggering of earthquakes during the 2000 Papua New Guinea earthquake sequence

A sequence of large earthquakes occurred in the New Britain/New Ireland region of Papua New Guinea in late 2000. The sequence started with a Mw 6.8 earthquake along the New Britain Trench on 29 October. About 20 days later a Mw 8.2 earthquake occurred in the New Ireland region on 16 November and produced large strike‐slip surface displacements and tsunamis. Following the Mw 8.2 event, two large earthquakes (Mw ∼ 7.5) occurred along the nearby New Britain Trench on 16 and 17 November. Furthermore, small triggered events were observed over a wide area outside of the rupture zones of the large earthquakes, with different focal mechanisms from those of the major events. There is likely some mechanism(s) that triggered this remarkable sequence, and we document the details of the spatial and temporal patterns of the events. We investigated if static stress changes can explain the initiation of the large earthquakes and also some groups of triggered smaller events. There are mixed results. The occurrences of the two M ∼ 7.5 major events may be explained by the static stress changes; however, there are also some earthquakes that are not consistent with triggering by static stress changes. There may be multiple mechanisms, including static and dynamic stress changes, that are needed to explain the complicated sequence of earthquakes.

Optical projection and image processing approach for mine wall monitoring

Wall movement in an underground mine must be continually monitored to provide real-time assessment of dynamic stress changes around mining excavation and to warn against rock failure. An in situ approach using optical spot projection and image processing can measure submillimeter movements. The system can be easily automated and poses no obstruction to mine traffic. The position of an off-normal laser spot will shift as the target wall moves. The centroid of this projected spot can be measured through image processing of a digital image. Multiple laser spots give the system simultaneous information over a larger sampled area. Software processing can measure subpixel shifts of the spot centroid. The resolution depends on the pixel count, the magnification of the camera lens (and hence the field of view), the optical-beam angle, and the spot characteristics. A laboratory table-top experiment demonstrated the system for distances up to 3 m and for a resolution of 0.1 mm. The results were linear in target movement, with standard errors between 0.83% and 5.38%. An automated system is described for a mine environment.

Stability of frictional slipping at an anisotropic/isotropic interface

The stability of steady, quasi-static slip at a planar interface between an anisotropic elastic solid and an isotropic elastic solid is studied. The paper begins with an analysis of anti-plane sliding at an orthotropic/isotropic interface. Friction at the interface is assumed to follow a rate- and state-dependent law. The stability to spatial perturbations of the form exp(i kx 1), where k is the wavenumber and x 1 is the coordinate along which the interface is studied. An expression is derived for the critical wavenumber ∣ k∣ cr above which there is stability. In-plane sliding at an anisotropic/isotropic interface is subsequently studied. In this case, slip couples with normal stress changes and a constitutive law for dynamic normal stress changes is adopted. Again a formula for ∣ k∣ cr is derived and the results are specialized to the case of an orthotropic/isotropic interface. Numerical plots of the dependence of ∣ k∣ cr on the orientation of the orthotropic solid, as well as on the material parameters are provided.

Spontaneous rupture processes on a bending fault

We simulated spontaneous rupture processes on a vertical, bending strike slip fault in a three‐dimensional half space, using a finite‐difference method. Rupture area and overall slip distribution on the fault vary with the initial stress field, which depends on strike change at the bend. Rupture velocity and detailed slip distribution around the bend, on the other hand, are affected by time‐dependent normal stress change caused by rupture. This dynamic stress change plays an important role in the rupture process ahead of the bend, as well as in the resulting ground motion. The numerical simulation method demonstrated here in a simplified geometry is equally applicable to modeling strong ground motion from geometrically complex ruptures in realistic earth models.

On the Role of Multiple Interactions in Remote Aftershock Triggering: The Landers and the Hector Mine Case Studies

The observed seismicity rate increase after large earthquakes in sites that are located several source lengths away from the mainshock centroid poses a major problem. This is because the static stress change induced by a mainshock in that region seems to be insignificant, and the dynamic stress changes can only en- hance the seismicity during the passage of the seismic waves but not at later times. In quest for a physically viable triggering mechanism for delayed aftershocks in remote sites, we examine earthquake activities in remote sites that were triggered by two California earthquakes, the magnitude 7.1 Hector Mine earthquake and the mag- nitude 7.3 Landers earthquake. We introduce a new method for quantifying the de- gree to which the triggering effect of each aftershock is locally more important than the triggering effect of the mainshock. We apply this method to the Landers and the Hector Mine remote aftershock sequences. We show that multiple stress transfers from early aftershocks to later aftershocks played an important role in the enhance- ment of both the Landers and the Hector Mine aftershock activities in remote sites. We present a time-space diagram of the Hector Mine remote aftershock sequence in the Imperial Valley, which shows that this sequence is made up of several subse- quences and that the onset of activity migrated southward.

Reply to "Comment on 'Lisbon 1755: A Case of Triggered Onshore Rupture?' by Susana P. Vilanova, Catarina F. Nunes, and Joao F. B. D. Fonseca," by L. Matias, A. Ribeiro, M. A. Baptista, N. Zitellini, J. Cabral, P. Terrinha, P. Teves-Costa, and J. M. Miranda

In Vilanova et al. (2003), referred to in the sequence as “the article,” we suggested that several observations pertaining to the historical accounts of the 1755 Lisbon earthquake are better explained assuming the occurrence of a triggered onshore rupture near Lisbon, a few minutes after the main earthquake. Such observations include the distribution of intensities and the high values in and around Lisbon, the occurrence of an early tsunami-like wave inside the Tagus lagoon prior to the arrival of the external tsunami, a report of ground deformation near Lisbon, cartographic evidence of changes in the course of the Tagus river, and the distribution of destructive aftershocks. The proposed location of the triggered rupture is the well-established seismogenic Lower Tagus Valley (ltv) fault (Cabral, 1995). There is reasonable consensus that the Lisbon earthquake was composed of three shocks in quick succession (Reid, 1914). The main innovation introduced in the article is the thesis that the location of one of the subevents was close to Lisbon, at a significant distance from the first shock. The distance between the classical Gorringe Bank epicenter (Machado, 1966) and the ltv fault is about 350 km, but this value can be significantly reduced by taking into account the finite length of the offshore rupture or by adopting a source closer to the coast as proposed in recent literature (Zitellini et al. , 1999). In view of the progress in the understanding of fault interaction through dynamic or static stress changes, we believe that our hypothesis is plausible, besides it is effective as a way of explaining the observations. L. Matias and colleagues, next referred to as “the comment,” claim that our conclusion is speculative and unsubstantiated, arguing that each anomalous observation reported in the article can be explained in a way that is different from …

Triggering of tsunamigenic aftershocks from large strike‐slip earthquakes: Analysis of the November 2000 New Ireland earthquake sequence

The November 2000 New Ireland earthquake sequence started with a Mw = 8.0 left‐lateral main shock on 16 November and was followed by a series of aftershocks with primarily thrust mechanisms. The earthquake sequence was associated with a locally damaging tsunami on the islands of New Ireland and nearby New Britain, Bougainville, and Buka. Results from numerical tsunami‐propagation models of the main shock and two of the largest thrust aftershocks (Mw > 7.0) indicate that the largest tsunami was caused by an aftershock located near the southeastern termination of the main shock, off the southern tip of New Ireland (Aftershock 1). Numerical modeling and tide gauge records at regional and far‐field distances indicate that the main shock also generated tsunami waves. Large horizontal displacements associated with the main shock in regions of steep bathymetry accentuated tsunami generation for this event. Most of the damage on Bougainville and Buka Islands was caused by focusing and amplification of tsunami energy from a ridge wave between the source region and these islands. Modeling of changes in the Coulomb failure stress field caused by the main shock indicate that Aftershock 1 was likely triggered by static stress changes, provided the fault was on or synthetic to the New Britain interplate thrust as specified by the Harvard CMT mechanism. For other possible focal mechanisms of Aftershock 1 and the regional occurrence of thrust aftershocks in general, evidence for static stress change triggering is not as clear. Other triggering mechanisms such as changes in dynamic stress may also have been important. The 2000 New Ireland earthquake sequence provides evidence that tsunamis caused by thrust aftershocks can be triggered by large strike‐slip earthquakes. Similar tectonic regimes that include offshore accommodation structures near large strike‐slip faults are found in southern California, the Sea of Marmara, Turkey, along the Queen Charlotte fault in British Columbia, and near the Alpine fault of New Zealand. Results from this study and previous stress modeling studies suggest that the likelihood of local tsunamis in these regions may significantly increase after a great strike‐slip earthquake.

Secrets of the code: Do vascular endothelial cells use ion channels to decipher complex flow signals?

The ability of vascular endothelial cells (ECs) to respond to changes in blood flow is essential for both vasoregulation and arterial wall remodelling, while abnormalities in endothelial responsiveness to flow play an important role in the development of atherosclerosis. Endothelial flow responses also have important implications for the field of vascular tissue engineering. In response to changes in fluid dynamic shear stress, ECs exhibit humoral, metabolic, and structural responses. Significantly, ECs respond differently to different types of shear stress. For instance, steady shear stress elicits a profile of responses that differs drastically from oscillatory shear stress. Although our understanding of flow-induced signaling has advanced greatly over the past two decades, how ECs sense shear forces remains to be established. Furthermore, the mechanisms by which ECs discriminate among different flow waveforms are unknown. Activation of flow-sensitive ion channels is one of the most rapid known responses to flow in ECs. In this paper, we argue in favor of an important role for ion channels in shear stress sensing in ECs and propose that these channels may endow ECs with the ability to resolve components of a complex flow signal and hence distinguish among different types of flow.

Slip‐generated patterns of swarm microearthquakes from West Bohemia/Vogtland (central Europe): Evidence of their triggering mechanism?

We investigated space‐time relations between consecutive events of West Bohemian 2000 swarm and their association with the Coulomb stress changes induced on a fault plane by prior swarm events. A few thousand M ≤ 3.3 strike‐slip swarm earthquakes clustered along a fault plane at depths 6.5–10.5 km and showed common rake angle of 30°. In order to disclose earthquake interaction we investigated the space‐time relations between consecutive earthquakes. We determined relative position vectors for each consecutive event pair, the prior event and the immediate aftershock (IA), and we measured time lags between them. The resulting cluster of relative position vectors shows a high density of aftershocks near the origin, which decays with distance. It points out a triggering effect of the prior event upon subsequent aftershocks. The spatial distribution of the relative positions disclosed dominance of aftershocks in the slip‐parallel directions, which is manifested by pronounced elongation of the cluster of the relative positions and of the angular dependence of the rate of IAs. The temporal distribution of the relative positions indicates that some aftershocks prove high interevent velocities and occur systematically at greater distances, suggesting the existence of two distinct triggering mechanisms acting at large and small timescales. We evaluated the complete Coulomb stress change upon the fault plane due to the prior event and showed that the observed space‐time distribution of the relative positions can be explained by a common effect of both static and dynamic stress changes, which act on different distance and timescale.