Strain Release Rate Research Articles

A Semi-theoretical criterion based on the combination of strain energy release rate and strain energy density concepts (STSERSED): Establishment of a new approach to predict the fracture behavior of orthotropic materials

Motivated by previous research performed by the authors assessing the fracture behavior in orthotropic materials under mixed-mode I/II loading, this article aims to propose a novel Semi-theoretical criterion for desired crack-fiber angles to assess the fracture of composite materials. Contrary to all previously proposed fracture criteria, in this criterion a mid-point experimental data related to the mixed-mode I/II loading is employed instead of mode I fracture toughness. Utilizing an arbitrary combination of mixed-mode I/II experimental data leads to a significantly simple and accurate fracture assessment criterion. More accurate estimation is achieved using more experimental data in mixed-mode I/II. For the first time, due to the importance of providing a fracture criterion, a Semi-theoretical criterion based on a combination of Strain Energy Release Rate (SER) and Strain Energy Density (SED) criteria, namely STSERSED, is adopted for more accurate anticipating of the fracture of orthotropic materials. Using SED criterion, mode I fracture toughness is theoretically derived and substitutes in the equations of maximum strain release rate. Furthermore, fitting mid-point experimental data into the presented criterion compensate the portion of wasted energy due to the creation of Fracture Process Zone (FPZ) and therefore more accurate fracture estimation is possible. With the passage of pure mode I and the emergence of mode II, the effects of FPZ increase, so changing the critical point from pure mode I to mid-point experimental data makes the extracted fracture behavior closer to the experimental data. Due to using experimental data and the relevant theoretical criterion simultaneously, this criterion can be used in engineering applications to extract the crack behavior of orthotropic materials. The verification of the STSERSED criterion is evaluated by comparing the fracture limit curves (FLC’s) with the available experimental data. The extracted results based on the proposed criterion highlight the achievement of this criterion to assess the fracture of orthotropic materials.

Temperature memory effect of stress annealing-induced anisotropy in metallic glasses

Stress annealing (SA)-induced magnetic anisotropy is known in iron, nickel, and cobalt-based ferromagnetic metallic glass ribbons and it has already been used in commercial processes. Uniaxial elastic strain is introduced by SA and is quenched into the ribbons even after cooling and removing the external stress. The release of the uniaxial quenched strains is clearly observed as an anomaly in the linear thermal-expansion coefficient (LTEC) when the ribbon is reheated without stress. The rate of strain release corresponding to the LTEC anomaly reaches a maximum at the temperature at which the original SA was performed. We have observed this temperature memory effect over the whole temperature range from 280 to 400 \ifmmode^\circ\else\textdegree\fi{}C, which is below the crystallization temperature ${T}_{x}$. The observed results are explained well by the existence of a localized ``flow unit'' embedded in an elastic matrix, which is accepted as the origin of the shear band formation and rejuvenation of metallic glasses with ${T}_{g}$ (glass transition temperature) $<{T}_{x}$. Although ${T}_{g}$ is hardly visible in calorimetry measurements in most of the ferromagnetic metallic glass ribbons (${T}_{g}>{T}_{x}$), the results here indicate that the same important structural feature is common to metallic glasses with both ${T}_{g}<{T}_{x}$ and ${T}_{g}>{T}_{x}$. Because magnetization behavior is very sensitive to the existence of residual elastic strain which is difficult to evaluate in most of the metallic glasses, detailed studies and a revival of interest in ferromagnetic ribbons will help us to understand more about the nature of the localized flow unit, as well as nonaffine deformations.

Slow slip events in the early part of the earthquake cycle

AbstractIn February 2014 a Mw = 7.0 slow slip event (SSE) took place beneath the Nicoya Peninsula, Costa Rica. This event occurred 17 months after the 5 September 2012, Mw = 7.6, earthquake and along the same subduction zone segment, during a period when significant postseismic deformation was ongoing. A second SSE occurred in the middle of 2015, 21 months after the 2014 SSE and 38 months after the earthquake. The recurrence interval for Nicoya SSEs was unchanged by the earthquake. However, the spatial distribution of slip for the 2014 event differed significantly from previous events, having only deep (~40 km) slip, compared to previous events, which had both deep and shallow slip. The 2015 SSE marked a return to the combination of deep plus shallow slip of preearthquake SSEs. However, slip magnitude in 2015 was nearly twice as large (Mw = 7.2) as preearthquake SSEs. We employ Coulomb Failure Stress change modeling in order to explain these changes. Stress changes associated with the earthquake and afterslip were highest near the shallow portion of the megathrust, where preearthquake SSEs had significant slip. Lower stress change occurred on the deeper parts of the plate interface, perhaps explaining why the deep (~40 km) region for SSEs remained unchanged. The large amount of shallow slip in the 2015 SSE may reflect lack of shallow slip in the prior SSE. These observations highlight the variability of aseismic strain release rates throughout the earthquake cycle.

A constitutive model of shape memory polymers based on glass transition and the concept of frozen strain release rate

Shape memory polymers (SMPs) are a type of polymeric smart material. They can maintain a deformed shape and return to their original shape according to external stimuli, such as temperature, light, pH, magnetic field and so on. In the last decade, SMPs have gained increasing attention due to their unique properties and have thus led great progress in developing proper constitutive models. In this paper, we propose and establish a new phase-evolution-based thermomechanical constitutive model for amorphous SMPs by considering the materials as a mixture of the rubbery phase and glassy phase. The shape memory effect (SME) is captured under the assumption that the rubbery phase can transform into the glassy phase and that part of the strain will be frozen during the glass transition. To make the model be more feasible, furthermore, we improve the model by introducing a time factor and considering the influence of frozen strain release rate. To validate the robustness and applicability of the proposed new model, we reproduce the shape memory behaviors (SMBs) of two different materials under different constraints and conditions. The results show a remarkable consistency between the new model simulation and experimental data.

Time–Space Evolution of Seismic Strain Release in the Area Shocked by the August 24–October 30 Central Italy Seismic Sequence

In this study, we analyze the space–time evolution of the seismic strain release in the area shocked by the still ongoing Italian Central Apennines seismic crisis started on August 24, 2016 and culminated with the October 30 main shock of Mw 6.5. Specifically, we examine the variation in time and space of the seismic strain release rate with the aim of identifying the presence of peculiar seismicity patterns, such as seismic gaps, according to the seismic cycle theory. To this end, seismic strain rates are checked for consistency with strain rates from GPS measurements to possibly adjust them for missing events due to limited seismic catalog extension or incompleteness at large magnitudes. Our results has revealed that the seismic crisis followed a long-term quiescence of about 310 years, characterized by the absence of M6.5+ earthquakes, and marked by an almost steady release of seismic deformation. Such temporal gap started after the occurrence of two nearby strong events in 1703 (Valnerina and L’Aquila earthquakes with magnitudes of 6.9 and 6.7, respectively) and terminated with the beginning of the current Central Apennines seismic crisis.

The unusual temporal and spatial slip history of the Wassuk Range normal fault, western Nevada (USA): Implications for seismic hazard and Walker Lane deformation

We document temporal and spatial variations in vertical displacement rate across 6 temporal orders of magnitude to better understand how the 100-km-long, east-dipping Wassuk Range normal fault system has accommodated strain in the context of the Walker Lane, a tectonically active, NNW-trending zone of dextral and extensional deformation that affects significant portions of western Nevada and eastern California. We combine 10 Be and 26 Al cosmonuclide exposure ages with shallow seismic and gravity data from the buried hanging wall of the Wassuk fault to derive a post–113 ka (10 5 yr time scale) vertical displacement rate of 0.82 ± 0.16 mm/yr. We also perform large-scale fault scarp analysis to constrain the long-term (>1 Ma; 10 6 yr time scale) displacement rate. Our fault-scarp analysis results imply similar vertical displacement rates, with higher long-term vertical displacement rates along the southern fault (∼1.1 mm/yr) relative to the northern fault ( Vertical displacement rate data at the 10 6 , 10 5 , 10 3 , and 10 1 yr time scales (this study and others) support a constant vertical displacement rate between 0.75 and 1.0 mm/yr for the Wassuk Range fault since ca. 4 Ma. An anomalously high vertical displacement rate at the 10 4 yr time scale is best explained by an earthquake cluster between ca. 15.5 ka and ca. 10.5 ka, potentially linked to rapid filling of the Walker Lake basin immediately prior to the ca. 13 ka Sehoo highstand of ancestral Lake Lahontan. We hypothesize that this flood event induced seismicity by placing an additional load on the hanging wall of the Wassuk Range fault and by increasing the pore-fluid pressure within and adjacent to the fault. Although an earthquake cluster like this is consistent with Wallace-type fault behavior, we suggest that a nontectonic stressor induced the cluster, resulting in the apparent discrepancy in vertical displacement rate at the 10 4 yr time scale. Thus, we posit that the long-term slip along Wassuk fault is better explained by slip-predictable Reid-type behavior, which deviates from the behavior of other well-documented fault systems. Based on these results, we suggest that similar, unrecognized nontectonic stressors may influence rates of strain release along other major fault systems worldwide. Finally, we present a revised model of central Walker Lane kinematics, based on data from this and other recent studies.

Influence of High Energy Electromagnetic Pulses on the Dynamics of the Seismic Process Around the Bishkek Test Area (Central Asia)

Investigation of dynamical features of the seismic process as well as the possible influence of different natural and man-made impacts on it remains one of the main interdisciplinary research challenges. The question of external influences (forcings) acquires new importance in the light of known facts on possible essential changes, which occur in the behavior of complex systems due to different relatively weak external impacts. Seismic processes in the complicated tectonic system are not an exclusion from this general rule. In the present research we continued the investigation of dynamical features of seismic activity in Central Asia around the Bishkek (Kyrgyzstan) test area, where strong electromagnetic (EM) soundings were performed in the 1980s. The unexpected result of these experiments was that they revealed the impact of strong electromagnetic discharges on the microseismic activity of investigated area. We used an earthquake catalogue of this area to investigate dynamical features of seismic activity in periods before, during, and after the mentioned man-made EM forcings. Different methods of modern time series analysis have been used, such as wavelet transformation, Hilbert Huang transformation, detrended fluctuation analysis, and recurrence quantification analysis. Namely, inter-event (waiting) time intervals, inter-earthquake distances and magnitude sequences, as well as time series of the number of daily occurring earthquakes have been analyzed. We concluded that man-made high-energy EM irradiation essentially affects dynamics of the seismic process in the investigated area in its temporal and spatial domains; namely, the extent of order in earthquake time and space distribution increase. At the same time, EM influence on the energetic distribution is not clear from the present analysis. It was also shown that the influence of EM impulses on dynamical features of seismicity differs in different areas of the examined territory around the test site. Clear changes have been indicated only in areas which, according to previous researches, have been characterized by anomalous increase of average rates of strain release and thus can be regarded as close to the critical state.

Stress and Strain in the Sweet Cherry Skin

Rain-cracking of sweet cherry (Prunus avium L.) fruit involves failure of the exocarp caused by excessive stress and strain. The objective of our study was to quantify exocarp strain in developing cherries. The release of linear elastic strain was followed in vivo using a gaping assay, whereas the release of biaxial elastic strain was followed in vitro after excision of small exocarp segments (ESs) that were submerged in silicone oil and strain release quantified by image analysis. When mature sweet cherry fruit were cut (by making two or more deep, longitudinal incisions parallel to the stylar/pedicel axis and on opposing sides of the fruit down to the pit), the incisions rapidly “gaped.” The gaping wounds continued to widen as they progressively released the linear elastic strain in the skin. By 24 hours the combined widths of two gapes represented 8.8% ± 0.1% of the fruit circumference. Increasing the number of cuts from two to 12 increased the cumulative gape widths to 14.9% ± 0.2%. In ES, monitoring the time course of relaxation after excision revealed a rapid release of biaxial strain, having a half-time of ≈2.7 minutes. Relaxation continued, but at a decreasing rate, for up to 48 hours. Across eight cherry cultivars, the biaxial strain in the exocarp at maturity ranged from 18.7% ± 1.9% in ‘Lapins’ to 36.0% ± 1.8% in ‘Katalin’. Elastic strain in the ES was always lower than that measured in an isolated cuticular membrane (CM). Increasing the temperature from 2 to 35 °C increased the rate of strain release and also the total percent strain released at 96 hours. In developing ‘Hedelfinger’ sweet cherry fruit, there was essentially no elastic strain in the exocarp at 45 days after full bloom (DAFB). Thereafter, significant elastic strain developed, reaching a maximum of 47.6% ± 2.5% at 87 DAFB. The effect of exocarp cell turgor on strain in the ES (evidenced by the difference in the reversible strain between ES with and without turgor) was closely and positively related to the relative area growth rate of the skin (r2 = 0.957). Strain release peaked at ≈59 DAFB, and there was no effect of turgor on strain release in mature fruit. Our data demonstrated the following: 1) the exocarp is a viscoelastic material composite; 2) at maturity, plastic and elastic strain components make up 66% and 34% of the total percent strain, respectively; 3) elastic strain in the exocarp increases during Stage III development; and 4) the strain in the exocarp is unaffected by strain in the CM. Thus, the epidermis and hypodermis layers must represent the main, load-bearing structure in sweet cherry fruit with the cuticle making a mechanically insignificant contribution.

Experimental development of fatigue delamination threshold criterion

The aim of this study was to develop a semi-empirical criterion capable of predicting the fatigue threshold delamination under varying mixed-mode ratio. To validate this criterion, a series of fatigue delamination tests in a unidirectional glass/epoxy composite were carried out at pure mode I, pure mode II, and different mixed modes. These tests were conducted using DCB (mode I), ENF (mode II), and MMB (mixed mode (I+II)) specimens. The experimental results have been expressed in terms of the total strain energy release rate thresholds GTth which correspond to no delamination growth after 106 cycles. They were correlated with the semi-empirical fatigue criterion through the plot of the total strain release rate thresholds ΔGTth versus the GIIGT modal ratio.

A late Holocene slip rate for the central North Anatolian fault, at Tahtaköprü, Turkey, from cosmogenic 10Be geochronology: Implications for fault loading and strain release rates

Measurement of a stream offset and cosmogenic dating (10Be) of the alluvial surface into which the stream incised yield a preferred late Holocene slip rate of 18.6 +3.5/−3.3 mm a−1 for the central part of the North Anatolian fault (NAF) at Tahtaköprü, Turkey; use of variable cosmogenic production rate (VPR) models yields a slightly slower rate of ∼16.4 +6.4/−4.5 mm a−1. The offset drainage (Karanlık Dere), which flows southward almost perpendicular to the east‐west trace of the NAF at the site, is displaced right laterally by 55 ± 10 m, with no vertical displacement. A 10Be age of ∼3 ka (∼3.5 ka VPR) from the top of a boulder on the best preserved part of the incised alluvial surface provides the most reliable maximum age for the onset of incision; 11 10Be ages from cobbles collected from the cultivated surface to the south yield younger ages, consistent with exhumation, erosion, and mechanical mixing during plowing. Our 18.6 +3.5/−3.3 mm a−1 rate is similar to other geologic slip rates measured along the NAF, all of which cluster between 15 and 20 mm a−1 over a wide range of (103–105) timescales. All of these geological rates, however, are slower than the ∼25 ± 2 mm a−1 short‐term rate of elastic strain accumulation measured geodetically. This disparity suggests the possibility that the NAF is experiencing a strain transient in which the lower crust beneath the fault is deforming faster than its long‐term rate.

Late Pleistocene slip rate along the Owens Valley fault, eastern California

The Owens Valley fault zone (OVF) is one of the primary structures accommodating dextral shear across the Eastern California shear zone (ECSZ). Previous estimates of the Holocene slip rate along this structure rely on paleoseismic data and yield rates 2–3 times lower than those implied by geodetic velocities. Using displaced lava flows along the flank of Crater Mountain, we present the first estimate of slip rate along the OVF during the late Pleistocene. Subsurface characterization of the flow margin using a ground‐penetrating radar (GPR) allows for relatively precise determination of dextral displacement, and terrestrial cosmogenic 36Cl exposure ages of samples from the flow surface yield slip rates between ∼2.8 – 4.5 mm/yr over the past 55–80 kyr. Our results suggest either that paleoseismic slip‐rate estimates underestimate the long‐term slip rate or that rates of strain release have not been steady during the latter part of the Quaternary.

Late Holocene slip rate for the North Anatolian fault, Turkey, from cosmogenic 36Cl geochronology: Implications for the constancy of fault loading and strain release rates

Geomorphologic mapping and cosmogenic radionuclide (36Cl) dating of an offset fluvial terrace yield a preferred late Holocene slip rate of 20.5 ± 5.5 mm/yr for the central part of the North Anatolian fault, Turkey; an independent slip rate constrained by 14C ages is 20.5 ± 8.5 mm/yr. These rates are generally similar to, but possibly slightly slower than, the short-term rate of elastic strain storage of 25 ± 1 measured geodetically across this major strike-slip fault ([Reilinger et al., 2006][1]), suggesting that loading and strain release on this part of the North Anatolian fault have been relatively constant when averaged over the past ∼2–2.5 k.y. We attribute this consistency to the relatively simple structure of the Anatolia-Eurasia plate boundary in north-central Turkey, where almost all plate boundary strain is accommodated along the North Anatolian fault. The absence of other moderate to high slip rate faults (and the earthquakes they produce) leads to a relatively simple stress evolution for the fault dominated by steady tectonic loading. [1]: #ref-10

ＤＣＢ試験片を用いた塗装鋼板の塗膜／鋼板界面の破壊じん性評価

A method for evaluating the interfacial adhesion strength between paint layer and chromate-coated steel sheet in the paint-coated steel sheet system was proposed. Three kinds of the steel sheets modified with chromic acid which contained various content of colloidal silica and a paint composed of a mixture of alkyd resin and silica particles were used as specimens for the experiment. The adhesion strength was evaluated by the critical strain energy release rate at interfacial crack initiation. To measure the critical strain energy release rate, an asymmetric double cantilever beam specimen was used, where an interfacial pre-crack was induced between the paint layer and steel sheet. When the crack propagates along the interface between paint layer and chromate-coated steel sheet, it was observed that the critical strain release rate increase with increasing the content of colloidal silica in the chromate-coated steel sheet. Similar dependency of the silica content on the adhesion strength had been also confirmed in the cross cut tests. This signified that the interfacial adhesion strength could be evaluated quantitatively by the critical energy release rate.

Cohesive and continuum damage models applied to fracture characterization of bonded joints

In this work, two different methods for simulating damage propagation are presented and applied to fracture characterization of bonded joints in pure modes I and II. The cohesive damage model is based on a special developed interface finite element including a linear softening damage process. In the continuum damage model the softening process is performed by including a characteristic length associated with a given Gauss point. The models were applied to the simulation of “ double cantilever beam” (DCB) and “ end notched flexure” (ENF) tests used to obtain the critical strain release rates in mode I and II of bonded joints. In mode I it was observed, under certain conditions, a good agreement between the results obtained by the two models with the reference value of critical strain energy release rate in mode I ( G Ic ) , which is an inputted parameter. However, in mode II some discrepancies on the obtained G IIc values were observed between the two models. These inaccuracies can be explained by the simplifying assumptions inherent to the cohesive model. Better results were achieved considering the crack equivalent concept.

The estimate of the effect of z-pins on the strain release rate, fracture and fatigue in a composite co-cured z-pinned double cantilever beam

The paper illustrates the effect of z-pins on the strain energy release rate in composite co-cured double cantilever beams (DCB) subject to a standard fracture toughness test. The conclusions obtained as a result of the solution illustrate that z-pins can provide drastic enhancement in fatigue and fracture properties of a co-cured z-pinned composite joint, even if their volume fraction is low. The strain energy release rate for loading and geometry combinations that do not result in immediate fracture was significantly reduced as a result of using z-pins. This slows the rate of the crack propagation if it is governed by the Paris law. Moreover, z-pins can completely arrest the crack. Although the analysis was performed for DCB specimens, the conclusions can be extrapolated to a general case of co-cured z-pinned joints.

Fracture Mechanics of Piezoelectric Materials

Fracture Mechanics of Piezoelectric Materials

A Systematic Investigation of Strain Relaxation, Surface Morphology and Defects in Tensile and Compressive InGaAs/InP Layers

AbstractThe results of a systematic investigation by transmission electron microscopy (TEM), cathodoluminescence (CL), Rutherford backscattering (RBS), X-ray diffraction and topography and scanning force microscopy (SFM) techniques on several InGaAs/InP compressive and tensile strained layers covering the misfit range from −2.3 to 1.5×10−2 and grown by the metal organic vapor phase epitaxy (MOVPE) technique are reported. In compressively strained films the same dependence for the residual strain vs the film thickness as for the InGaAs/GaAs is found whereas a different strain release rate and different extended defects are found in tensile stressed InGaAs alloy. In particular in tensile stressed samples, grooves, planar defects and cracks are present in addition to the interfacial network of misfit dislocations. The correlation between the observed planar defects and the mechanisms of strain relaxation in the case of tensile strained layers is discussed.

Material Design for High Strength of Continuous Fiber-Reinforced and Reaction-Sintered SiC Matrix Composites by Paying Attention to Fiber-Pullout Behavior.

Interfacial debonding behaviors between fiber and matrix in continuous fiber-reinforced reaction-sintered SiC matrix composites have been analyzed in terms of strain energy release rate using a finite element method. In particular, the effects of Young's modulus ratio, Em/Ef, and fiber volume fraction, Vf, on the strain energy release rate have been investigated. As a result, it was confirmed that the steady-state strain release rate increased with increasing the Young's modulus ratio and decreasing the fiber volume fraction. Also, it was clarified that the quasi-yield state like carbon steels observed in stress-strain curve was explainable by the strain energy release rate of interfacial debonding between fiber and matrix.

Frequency of occurrence of moderate to great earthquakes in intracontinental regions: Implications for changes in stress, earthquake prediction, and hazards assessments

We investigate the departure of shallow intracontinental earthquakes from the frequency‐magnitude relationship log (n(M)) =a‐bM. We consider seven large continental regions but exclude subduction zones. In each, “active” and “stable” areas are differentiated. Within active areas we separately categorize earthquakes on faults with high slip rates. We use data sets from 1978–1994 and 1900–1994, which are complete for moment magnitudesMw≥5.3 and ≥7.0, to calculate changes inbvalue withMw. For all active intracontinental regions combined except Asia,bchanges at 98% confidence from 0.90 to 2.1 at a corner magnitudeMcof 6.9 to 7.0. The distribution for stable regions indicates a similar change. Values ofMcare associated with downdip widths of rupture of about 23 to 27 km, which are smaller than those for subduction zones. In each case,Mcmarks a transition from unbounded to bounded earthquakes. In Asia, events from 1958 to 1994 also delineate a similar change nearMc7.0. Earthquakes in Asia of 7.0≤Mw≤8.1 from 1900 to 1957, however, define abvalue of 1.0 and a moment release rate 5.6 times higher than that from 1958 to 1994. Those anomalous values indicate that a large region of Asia was close to failure, i.e., near a self‐organized critical state, during the earlier period. We associate those changes with the giant Himalayan earthquake in 1950 ofMw8.6. Regional variations in seismic strain release rates correlate with the types of processes at adjacent plate boundaries. Extrapolating rates of activity of the past 95 years toMw≥8.0 indicates that such events should be very rare in stable areas.

Large mid-Holocene and late Pleistocene earthquakes on the Oquirrh fault zone, Utah

The Oquirrh fault zone is a range-front normal fault that bounds the east side of Tooele Valley and it has long been recognized as a potential source for large earthquakes that pose a significant hazard to population centers along the Wasatch Front in central Utah. Scarps of the Oquirrh fault zone offset the Provo shoreline of Lake Bonneville and previous studies of scarp morphology suggested that the most recent surface-faulting earthquake occurred between 9000 and 13,500 years ago. Based on a potential rupture length of 12 to 21 km from previous mapping, moment magnitude ( M w) estimates for this event range from 6.3 to 6.6 In contrast, our results from detailed mapping and trench excavations at two sites indicate that the most-recent event actually occurred between 4300 and 6900 yr B.P. (4800 and 7900 cal B.P.) and net vertical displacements were 2.2 to 2.7 m, much larger than expected considering estimated rupture lengths for this event. Empirical relations between magnitude and displacement yield M w 7.0 to 7.2. A few, short discontinuous fault scarps as far south as Stockton, Utah have been identified in a recent mapping investigation and our results suggest that they may be part of the Oquirrh fault zone, increasing the total fault length to 32 km. These results emphasize the importance of integrating stratigraphic and geomorphic information in fault investigations for earthquake hazard evaluations. At both the Big Canyon and Pole Canyon sites, trenches exposed faulted Lake Bonneville sediments and thick wedges of fault-scarp derived colluvium associated with the most-recent event. Bulk sediment samples from a faulted debris-flow deposit at the Big Canyon site yield radiocarbon ages of 7650 ± 90 yr B.P. and 6840 ± 100 yr B.P. (all lab errors are ±1 α). A bulk sediment sample from unfaulted fluvial deposits that bury the fault scarp yield a radiocarbon age estimate of 4340 ± 60 yr B.P. Stratigraphic evidence for a pre-Bonneville lake cycle penultimate earthquake was exposed at the Pole Canyon site, and although displacement is not well constrained, the penultimate event colluvial wedge is comparable in size to the most-recent event wedges. Charcoal from a marsh deposit, which overlies the penultimate event colluvium and was deposited during the Bonneville lake cycle transgression, yields an AMS radiocarbon age of 20,370 ± 120 yr B.P. Multiple charcoal fragments from fluvial deposits faulted during the penultimate event yield an AMS radiocarbon age of 26,200 ± 200 yr B.P. Indirect stratigraphic evidence for an antepenultimate event was also exposed at Pole Canyon. Charcoal from fluvial sediments overlying the eroded free-face for this event yields an AMS age of 33,950 ± 1160 yr B.P., providing a minimum limiting age on the antepenultimate event. Ages for the past two events on the Oquirrh fault zone yield a recurrence interval of 13,300 to 22,100 radiocarbon years and estimated slip rates of 0.1 to 0.2 mm/yr. Temporal clustering of earthquakes on the nearby Wasatch fault zone in the late Holocene does not appear to have influenced activity on the Oquirrh fault zone. However, consistent with findings on the Wasatch fault zone and with some other Quaternary faults within the Bonneville basin, we found evidence for higher rates of activity during interpluvial periods than during the Bonneville lake cycle. If a causal relation between rates of strain release along faults and changes in loads imposed by the lake does exist, it may have implications for fault dips and mechanics. However, our data are only complete for one deep-lake cycle (the past 32,000 radiocarbon years), and whether this pattern persisted during the previous Cutler Dam and Little Valley deep-lake cycles is unknown.