Frictional Overshoot Research Articles

Rise time of the 2018 MW 6.4 Hualien earthquake revealed by source time functions: A restrictive estimation of static stress drop

Using the ω−2 source model, the rise time of the 2018 Mw 6.4 Hualien earthquake is estimated from the corner frequency of the Fourier spectrum of the source time function. Two source parameters are also determined: average dynamic stress drop (∆σd) and static stress drop (∆σs). The results show that the rise time is 2.52 s, which is approximately 0.23 times the value of the entire source duration and then leads to a ∆σd of 3.03 MPa. In this study, we propose a method to confine the estimation of ∆σs through ∆σd. Because the radiated seismic energy exists, this leads to ∆σs<2∆σd−2μEgM0 (Eg is the fracture energy, M0 is the seismic moment, and μ is the rigidity) on average. Hence, we suggest that ∆σs for the 2018 Hualien earthquake should be less than 4.81 MPa. Because of ∆σs > ∆σd, the earthquake's rupture can be interpreted in a frictional overshoot model; then, the radiation efficiency near 0.5 suggests that 50% of the available energy is released to extend the fault. Furthermore, the lower fracture energy density (G) for the Hualien earthquake is probably due to the fact that an ML 5.9 foreshock disturbs the fault system beforehand.

Towards a plastic engine: Low—temperature tribology of polymers in reciprocating sliding

Fundamental tribological studies of a range of engineering polymers, including a bio-derived Polytrimethylene-terephthalate (PTT) have been conducted at low temperatures (12C∘ and −8C∘). The aim of the study was to replace a conventional honed aluminium liner/polytetrafluoroethylene (PTFE) seal interface with a polymer combination, within a Dearman Engine. The Dearman Engine is a novel piston engine driven by the expansion of a cryogenic fluid, either liquid nitrogen or liquid air, to produce emissions-free combined cooling and power. A tribometer was used to simulate engine conditions.The efficacy of the polymers relative to the honed aluminium benchmark was assessed in terms of a projected material transfer layer. The magnitude of which was determined using a combination of scanning electron microscope (SEM)/energy-dispersive X-ray spectroscopy (EDS) and Abbott—Firestone curves, a descriptor of surface texture. The concept of a frictional overshoot, correlated with the severity of wear measured on the PTFE specimen, is introduced.For the engine, a low coefficient of friction (CoF) leads to reduced parasitic losses and low wear will ensure the integrity of the piston seal is maintained, and so to the sealing capacity of the engine. Material transfer, generally from seal to liner specimens was detected in all but the unhoned polyoxymethylene (POM) and unhoned Aluminium samples. These two combinations had the lowest frictional overshoots and the lowest levels of wear. These are properties that were also linked to a low surface roughness and a low gradient of the interquartile range of the Abbott-Firestone curve. These materials both outperformed the benchmark seal/liner combination and the POM provides the potential for an all polymer expansion chamber.

Long-Term Evolution of the Deviatoric Background Stress in the Focal Region of the 2011 Tohoku-Oki Earthquake

On 11 March 2011, a giant interplate earthquake of magnitude Mw 9.1 struck Tohoku-Oki area in eastern Japan. The earthquake is acknowledged to have permanently altered the stress field in and around the focal region. To capture the temporal change of the overall stress field, I examined 1251 focal mechanisms, from the NIED MT catalog, that occurred before and after the Tohoku-Oki earthquake from January, 2006 to January, 2017 in the focal region near the subducting slab. The examined observations were grouped into six periods, and based on the selected NIED MT catalog, the stress regime in each period was obtained by using the damped stress tensor inversion method. Based on the temporal evolution of stress rotation, the corresponding deviatoric stress level was estimated using a simplified 2D model. Results of the 10-year seismic stress cycle show that several years before the Tohoku-Oki earthquake, the stress accumulation level seems to have experienced an acceleration process. Studies suggest that this increasingly critically stress state combined with the sufficiently reduced coupling rate off the Tohoku area finally resulted in the unprecedented megathrust event. The coseismic process was violent and released almost all of the deviatoric stress that presented before the main shock. The resultant stress state even reached frictional overshoot. Thus, the postseismic stress pattern in the source region was reshaped significantly, especially for the upper plate and updip portion of the lower plate. After the main shock near the rupture surface, a surprisingly rapid and high-level stress reloading occurred within several postseismic years. To reconcile the classical subduction zone earthquake generation cycle model, the event may be described as an instantaneously decoupled stress state between the upper and inner plates.

Estimation of earthquake source parameters in the Kachchh seismic zone, Gujarat, India, using three component S-wave spectra

Earthquake source parameters and crustal $$Q_{0}$$ values for the 138 selected local events of ( $$\hbox {M}_{\mathrm{w}}{:}2.5{-}4.4$$ ) the 2001 Bhuj earthquake sequence have been computed through inversion modelling of S-waves from three-component broadband seismometer data. SEISAN software has been used to locate the identified local earthquakes, which were recorded at least three or more stations of the Kachchh seismological network. Three component spectra of S-wave are being inverted by using the Levenberg–Marquardt non-linear inversion technique, wherein the inversion scheme is formulated based on $$\omega ^{2}$$ source model. SAC Software (seismic analysis code) is being utilized for calculating three-component displacement and velocity spectra of S-wave. The displacement spectra are used for estimating corner frequency (in Hz) and long period spectral level (in nm-s). These two parameters play a key role in estimating earthquake source parameters. The crustal $${Q}_{0}$$ values have been computed simultaneously for each component of three-component broadband seismograph. The estimated seismic moment ( $$M_{0}$$ ) and source radius (r) using S-wave spectra range from 7.03E+12 to 5.36E+15 N-m and 178.56 to 565.21 m, respectively. The corner frequencies for S-wave vary from 3.025 to 7.425 Hz. We also estimated the radiated energy ( $$E_{S}$$ ) using velocity spectra, which is varying from 2.76E+06 to 4.07E+11 Joules. The estimated apparent stress drop and static stress drop values range from 0.01 to 2.56 and 0.53 to 36.79 MPa, respectively. Our study also reveals that estimated $$Q_{0}$$ values vary from 119.0 to 7229.5, with an average $$Q_{0}$$ value of 701. Another important parameter, by which the earthquake rupture process can be recognized, is Zuniga parameter. It suggests that most of the Kachchh events follow the frictional overshoot model. Our estimated static stress drop values are higher than the apparent stress drop values. And the stress drop values are quite larger for intraplate earthquakes than the interplate earthquakes.

Evidence for non-self-similarity in the M w 7.7 2001 Bhuj earthquake sequence

Scaled energy, apparent stress, seismic moments, stress drops and corner frequencies are measured through the Levenberg–Marquardt nonlinear inversion modeling of S-wave displacement spectra for 489 selected earthquakes (M w 2.05–5.52) from the 2001 M w 7.7 Bhuj earthquake sequence. The iterative inversion scheme is formulated based on the ω-square source spectral model, which enabled us to estimate stable source parameters. The estimated seismic moment (M o ) and source radius (r) vary from 1.5 × 1012 to 2.4 × 1017 to N m and 139.1–933.9 m, respectively, while estimated stress drops (Δσ) and the multiplicative factor (E mo) values range from 0.1 to 14.4 MPa and 1.0–4.1, respectively. The corner frequencies (f c) are found to be ranging from 1.4 to 9.3 Hz. The mean standard deviation for f c, r and Δσ are estimated to be 0.7 Hz, 91.4 m and 2.9 MPa, respectively. The radiated seismic energy and apparent stresses range from 2.1 × 105 to 4.1 × 1013 Joule and 0.005–8.0 MPa, respectively. Our estimated corner frequencies and seismic moments satisfy the relation M o ∞ f c −(3+) , where e (measure for a deviation from self-similarity) is found to be 1.33 for the larger earthquakes (M o ≥ 2 × 1015 N m), while the parameter e is estimated to be 6.74 for smaller earthquakes (M o < 2 × 1015 N m). We feel that the larger value of e may require to satisfy the increasing trend of scaled energy with moment for smaller earthquakes. We also notice that stress drops increase with seismic moment, approximately as Mo3 (Δσ∝M o 3) for smaller events (M o < 1015.3 N m), while for larger earthquakes (M o ≥ 2 × 1015 N m) stress drop increases approximately with M 1 (Δσ∝M 1 ). Adding credence to this non-self-similar theory, our estimated seismic moments and source radii (r) also reveal a break in the linear self-similar source scaling at M o = 2 × 1015 N m and r = 300 m, which is attributed to constant source radius for smaller earthquakes. Further, a comparative study between apparent stresses and static stress drops suggests a probable frictional overshoot mechanism for larger earthquakes, while smaller shocks are showing both partial stress drop and frictional overshoot mechanisms. We hypothesize that larger events are probably subject to the regional state-of-stress and fluid flow in the fault zone, whereas smaller earthquakes are sensitive to the local state-of-stress associated with material heterogeneities and fluid flows within the fault zone. We also propose that the relations developed in this study could be useful for accessing proper seismic hazard in the region.

Bounding of near-fault ground motion based on radiated seismic energy with a consideration of fault frictional mechanisms

The energy radiated as seismic waves strongly depends on the fault rupture process associated with rupture speed and dynamic frictional mechanisms involved in the fault slip motion. Following McGarr and Fletcher approach, we derived a physics-based relationship of the weighted average fault slip velocity vs apparent stress, rupture speed and static stress drop based on a dynamic circular fault model. The resultant function can be approximately used to bound near-fault ground motion and seismic energy associated with near-fault coseismic deformation. Fault frictional overshoot and undershoot mechanisms governed by a simple slip-weakening constitutive relation are included in our consideration by using dynamic rupture models named as M- and D-models and proposed by Madariaga (1976) and Boatwright. We applied the above function to the 2008 great Wenchuan earthquake and the 1999 Jiji (Chi-Chi) earthquake to infer the near-fault ground motion called slip weighted average particle velocity and obtained that such model-dependent prediction of weighted average ground velocities is consistent to the results derived from the near-fault strong motion observations. Moreover, we compared our results with the results by McGarr and Fletcher approach, and we found that the values of the weighted average particle velocities we obtained for these two earthquakes are generally smaller and closer to the values by direct integration of strong motion recordings of the near-fault particle velocity waveform data. In other words, if this result comes to be true, it would be a straightforward way used to constrain the near-fault ground motion or to estimate source parameters such as rupture speed, static and dynamic stress drops.

Source Parameters of the 2005 Mw 7.2 Miyagi-Oki, Japan, Earthquake as Inferred from Teleseismic P-Waves

We investigate the fault parameters of the 2005 Miyagi-Oki (Japan) earthquake using duration variations of teleseismic P-waves. The results show that the earthquake has a thrust-type mechanism and a seismic moment of 4.46 × 10 19 Nm. Rupture directivity analysis suggests that the earthquake occurred as a result of a bilateral faulting on the fault plane with a strike of 247°, a dip of 17° and a slip of 125°. The optimal rupture azimuth, measured counterclockwise from the strike on the fault plane, is 170° (or 350°). The rupture length and average source duration are estimated to be 73.4 km and 14.5 sec, respectively. Thus the rupture velocity is 2.53 km sec -1 (~0.57 times the value of S-wave velocity), which is lower than the value for other similarly sized earthquakes. This implies that the 2005 Miyagi-Oki earthquake was probably a slow event. Consequently, there may have been less release of high-frequency seismic energy, leading to lower radiated seismic energy and radiation efficiency (~0.32 - 0.48). In other words, relatively larger fracture energy occurred during earthquake faulting in addition to the heat due to friction. The ratio of the static stress drop to the apparent stress (> 2.0) also suggests that the earthquake can be modeled as a frictional overshoot in a stress model, which implies the transformation of a lower percentage of strain energy into seismic-wave energy during the process of earthquake rupturing.

Constraints on rupture speed of the 2001 MS 8.1 West Kunlun Mountain Pass earthquake by co-seismic surface rupture slip displacements based on the slip-weakening mechanism with frictional undershoot involved

With co-seismic surface rupture slip displacements provided by the field observation for the 2001 MS8.1 West Kunlun Mountain Pass earthquake, this paper estimates the rupture speed on the main faulting segment with a long straight fault trace on the surface based on a simple slip-weakening rupture model, in which the frictional overshoot or undershoot are involved in consideration of energy partition during the earthquake faulting. In contrast to the study of Bouchon and Vallee, in which the rupture propagation along the main fault could exceed the local shear-wave speed, perhaps reach the P-wave speed on a certain section of fault, our results show that, under a slip-weakening assumption combined with a frictional undershoot (partial stress drop model), average rupture speed should be equal to or less than the Rayleigh wave speed with a high seismic radiation efficiency, which is consistent with the result derived by waveform inversion and the result estimated from source stress field. Associated with the surface rupture mechanism, such as partial stress drop (frictional undershoot) associated with the apparent stress, an alternative rupture mechanism based on the slip-weakening model has also been discussed.

Source parameters and stress release of seismic sequences occurred in the Friuli-Venezia Giulia region (Northeastern Italy) and in Western Slovenia

The source parameters of the major events of a swarm and of two seismic sequences, occurred in the Friuli area (Northeastern Italy) and in Western Slovenia, were estimated. The Claut swarm (C96) occurred since the end of January to June 1996, with a M D 4.3 major shock and it appears composed of three sub-sequences. The two sequences are the Kobarid sequence (K98) started on April 12, 1998 with a M D 5.6 mainshock and the M.te Sernio (S02) sequence caused by the February 14, 2002 earthquake ( M D = 4.9). Acceleration and velocity data recorded by the local seismic network of the Istituto Nazionale di Oceanografia e di Geofisica Sperimenale (OGS) and corrected for attenuation, were employed to estimate seismic moments and radiated energies. Source dimensions were inferred from the computed corner frequencies and the stress release was estimated from the Brune stress drop, the apparent stress and the RMS stress drop. On the whole, seismic moments range from 1.7 × 10 12 to 1.1 × 10 17 N m, and radiated energies are in the range 10 6–10 13 J. Brune stress drops are scattered and do not show any evidence of a self-similarity breakdown for sources down to 130 m radius. The radiated seismic energy scales as a function of seismic moment, with a slope of the scaling relation that decreases for increasing seismic moments. The mechanism of stress release was analyzed by computing the ɛ parameter of Zuniga [Zuniga, R., 1993. Frictional overshoot and partial stress drop. Which one? Bull. Seismol. Soc. Am. 83, 939–944]. The K98 and S02 sequences are characterized by a wide range of the ɛ parameter with stress drop mechanism varying from partial locking to overshoot cases. The ɛ values of the C96 swarm are more homogeneous and close to the Orowan's condition. The radiated seismic energy and the ratio of stress drop between mainshock and aftershocks appear different among the analyzed cases. We therefore investigated the relationship between the stress parameters of the main shock and the energy radiated by the aftershock sequences. For this purpose, we also estimated the source parameters of two other sequences occurred in the area, with mainshocks of M D 4.1 and 5.1, respectively. We found a positive correlation between the Brune stress drop of the mainshock and the ratio between the radiated energy of the mainshock and the summation of the energies radiated by the aftershocks.

Estimates of Stress Drop of the Chi-Chi, Taiwan, Earthquake of 20 September 1999 from Near-Field Seismograms

The apparent stress and stress drop of the Chi-Chi, Taiwan, earthquake are estimated from near-field seismograms. The estimated apparent stress and stress drop for the southern part of the fault are about 100 bars lower than those for the northern part. The estimated ratio E s/ M also suggests that there is a higher dynamic stress drop in the northern part than in the southern one. This indicates the transformation of a higher percentage of strain energy into the seismic-wave energy in the northern part than in the southern part. Based on a parameter proposed by Ramon Zuniga (1993), we propose that the stress model of frictional overshoot can interpret the rupture of the Chelungpu fault, on which the Chi-Chi, Taiwan, earthquake occurred. Manuscript received 31 July 2000.

Partial Stress Drop and Frictional Overshoot Mechanism of Seismic Events Induced by Mining

—The values of uniformly estimated apparent stress σa and Brune’s stress drop, taken as a measure of static stress drop, from 850 seismic events, with moment magnitude ranging from −3.6 to 3.6, induced at the Underground Research Laboratory (URL) in Canada, Western Deep Levels (WDL) gold mine in South Africa, and two coal and two copper mines in Poland, were collected to study the stress release mode in various mining environments. For this, the quantity epsilon, ɛ=Δσ/(σa + Δσ/2), where Δσ is the static stress drop, proposed by Zuniga (1993) as an indicator of stress-drop mechanism was used. The events induced at the URL are characterized by low values of epsilon corresponding to a partial stress drop mechanism, whereas all the events at WDL display a frictional overshoot mechanism in which final stress reaches a lower value than that of frictional stress. The events at Polish coal and copper mines, on the other hand, are in good agreement with the well-known Orowan’s condition such that the final stress is equal to the dynamic frictional stress.¶The Brune stress drop, however, is heavily model dependent through the source radius-corner frequency relation. The Orowan’s condition for the events from the URL would be met if a constant in the source radius-corner frequency relation is equal to 1.82 ± 0.12, and for the events from WDL if it is equal to 3.92 ± 0.40, in contrast to Brune’s constant of 2.34.¶The smoothed values of epsilon displayed as a function of time, represented by the consecutive event numbers, for selected sets of events imply that the largest seismic events in a given set occur when the epsilon is low and a partial stress drop mechanism is dominant. The large events are then followed by high epsilon values when a frictional overshoot mechanism begins to dominate.

Source parameters for the Roermond aftershocks of 1992 April 13-May 2 and site spectra for P and S waves at the Belgian seismic network

SUMMARY One- and three-component digital recordings from six stations of the Belgian seismic network were used to invert simultaneously for source velocity spectra of 18 aftershocks of the ML5.8 Roermond earthquake and for site amplification spectra at these stations. The events were selected to have well-constrained fault-plane solutions and the stations to be within 140 km epicentral distance. Frequency-dependent quality factors were computed from the coda waves of the same events. The Joint Source-Site Determination method we used, first corrects the body-wave spectra for radiation pattern, geometrical spreading, attenuation and free surface effect and then is formulated as a linear inverse problem repeated over frequencies (in this application between 1 and 30 Hz), with one reference station for which the site amplification spectrum is given as constant (in this application: La Chartreuse). The unbiased source velocity spectra were fitted with a Brune-type spectral function to obtain a scale factor and a corner frequency, from which, among others, the seismic moment, source radius, stress drop, final disolcation and fracture energy were calculated. In the 1.9-3.4 ML magnitude range, the stress drop, seismic energy and fault radius tend to increase with seismic moment, and seismic efficiency with fault dimension. Brune's stress drop varies between 0.4 and 4.6 MPa. Frictional overshoot prevails over partial stress drop. The average ratio of P- and S-wave corner frequencies is 1.6. The site amplification spectra vary between 1 and 10. Strong site effects were observed at stations Membach and Vianden.