Rupture Initiation Point Research Articles

Failure analysis of a ruptured compressor pressure vessel

This paper deals with failure analysis of a ruptured pressure vessel that served as a part of an air compressor. Pressure vessel failed during hydrostatic test when, at a pressure level lower than proof pressure, two cracks occurred on the shell and test fluid leakage was recorded. Experimental investigation methods were employed to determine possible causes of crack occurrence and vessel rupture. Liquid penetrate inspection was performed to check for other surface-breaking defects on the shell and locations of the cracks. Visual examination revealed the condition of the internal surface of the shell. Optical microscopy was used to inspect crack area while scanning electron microscopy examination at suitable magnification was employed to characterize fine microstructure of the fractured surface and to reveal flaws that served as rupture initiation points. Material’s chemical composition was determined using optical emission spectrometer with glow discharge source sample stimulation. Hardness test results were used to derive maximum tensile strength of the material. According to results obtained from performed investigations, it was concluded that excessive corrosion at the bottom part of the pressure vessel caused formation of pits that served as initiation points for leakage cracks. Recommendations for avoidance of such scenario with the rest of the user’s compressor pressure vessel were given. Also, ultrasonic testing of shell thickness was performed and results of the performed hydrostatic pressure test were recorded to be used in subsequent numerical failure analysis of the failed pressure vessel.

Development of high-performance superabsorbent polymers through the use of data science

We simulate the strong ground motion for an expected major earthquake (Mw 7.0) beneath the Bhutan Himalayan region with an empirical Green's function method using waveforms recorded from the 2009 Bhutan mainshock (Mw 6.1) and its largest aftershock (Mw 5.1). Fault orientation and location of the simulated event extend the length of the fault plane determined from the 2009 Bhutan mainshock and aftershock along its strike. The simulated PGA values are compared with the results derived from a ground motion prediction equation (GMPE) for the Himalayan region and it is found that different levels of accelerations are associated with different rupture initiation points on the fault plane. It is observed that the NE Indian region is capable of generating peak ground acceleration (PGA) in exceedance to 121 cm/s2 for simulated earthquake (Mw 7.0). The maximum impacts of shaking will be on the sites located near the rupture initiation points that are poised to generate higher values of ground acceleration. To validate our simulation, we also estimate the extent of rupture directivity of the simulated earthquake with respect to four initiation points indicating that higher value of PGA and shaking duration exist either to South or to South-West azimuths from the imitated locations, which are corroborated with respective geology of the sites. This study suggests that areas of maximum ground shaking would occur in the vicinity of the source initiation where possibility of relatively stronger earthquake hazards does exist, which in turn requires attention for adoption of earthquake risk mitigation plans in view of impacts of trans-boundary earthquakes in the region.

Simulation of Strong Ground Motion for an Mw 7.0 Earthquake beneath the Bhutan Himalaya in NE India and its trans-boundary seismic hazard implications

We simulate the strong ground motion for an expected major earthquake (Mw 7.0) beneath the Bhutan Himalayan region with an empirical Green's function method using waveforms recorded from the 2009 Bhutan mainshock (Mw 6.1) and its largest aftershock (Mw 5.1). Fault orientation and location of the simulated event extend the length of the fault plane determined from the 2009 Bhutan mainshock and aftershock along its strike. The simulated PGA values are compared with the results derived from a ground motion prediction equation (GMPE) for the Himalayan region and it is found that different levels of accelerations are associated with different rupture initiation points on the fault plane. It is observed that the NE Indian region is capable of generating peak ground acceleration (PGA) in exceedance to 121 cm/s2 for simulated earthquake (Mw 7.0). The maximum impacts of shaking will be on the sites located near the rupture initiation points that are poised to generate higher values of ground acceleration. To validate our simulation, we also estimate the extent of rupture directivity of the simulated earthquake with respect to four initiation points indicating that higher value of PGA and shaking duration exist either to South or to South-West azimuths from the imitated locations, which are corroborated with respective geology of the sites. This study suggests that areas of maximum ground shaking would occur in the vicinity of the source initiation where possibility of relatively stronger earthquake hazards does exist, which in turn requires attention for adoption of earthquake risk mitigation plans in view of impacts of trans-boundary earthquakes in the region.

Simulation of strong ground motion for 1905 Kangra earthquake and a possible megathrust earthquake (Mw 8.5) in western Himalaya (India) using Empirical Green’s Function technique

Earthquakes are deadliest among all the natural disasters. The areas that have experienced great/large earthquakes in the past may experience big event in future. In this study, we have simulated Kangra earthquake (1905, Mw 7.8) and a hypothetical great earthquake (Mw 8.5) in the north-west Himalaya using Empirical Green’s Function (EGF) technique. Recordings of Dharamsala earthquake (1986, Mw 5.4) are used as Green function with a heterogeneous source model and an asperity. It has been observed that the towns of Kangra and Dharamsala can expect ground accelerations in excess of 1 g in case of a Mw 8.5 earthquake and could have experienced an acceleration close to 1 g during 1905 Kangra earthquake. The entire study region can expect acceleration in excess of 100 cm/s2 in case of Mw 7.8 and 200 cm/s2 in case of Mw 8.5. The sites located near the rupture initiation point can expect accelerations in excess of 1 g for the magnitudes simulated. For validation, the estimates of the PGA for Mw 7.8 simulation are compared with isoseismal studies carried out in the same region after the Kangra earthquake of 1905 by converting PGA values to intensities. It was found that the results are comparable. The target earthquakes (Mw 7.8 and Mw 8.5) are simulated at depth of 20 km and 30 km to examine the effect of PGA for different depths. The PGA values obtained in the present analysis gave us an idea about the level of accelerations experienced in the area during 1905 Kangra earthquake. Future construction in the area can be regulated, and built environ can be strengthened using PGA values obtained in the present analysis.

Statistics of Ground Motions in a Foam Rubber Model of a Strike‐Slip Fault

Abstract The peak ground acceleration (PGA) and peak ground velocity (PGV) from 5058 ruptures of a foam rubber stick‐slip model are not distributed according to a lognormal probability distribution function. PGA and PGV values are decomposed using the method of Anderson and Uchiyama (2011). The statistically significant deviations from the lognormal distribution occur near the peak of the distribution. In some cases, high‐amplitude tails differ by a much greater ratio, but the statistical significance of this effect is low. This result is true of both raw data and data adjusted for site and magnitude. Event terms are also not lognormal but can be modeled as a sum of three or four lognormal subdistributions, which possibly represent different preferred rupture initiation points rather than a uniform distribution of initiation points. The event term subdistributions with highest median values have small standard deviations, so if shapes of this nature were used in ground‐motion prediction equations (GMPEs) during a probabilistic seismic‐hazard analysis, the effect of the long tail of the lognormal distribution in controlling the hazard would be weakened considerably. Static stress drop was recorded for each event, and event terms for PGA and PGV are well correlated with static stress drop. Unlike Next Generation Attenuation‐West 2 GMPEs, residual variances for the foam model are dominated by variability in the source slip function, rather than the path and site effects. This difference in the variance budget results from the way in which the source and site residuals are defined in this study; the source uncertainty includes variation in the rupture size (magnitude) and location, along with deviations in distance and path. We do not know if these results apply to earthquakes, but we do think tests of repeating stick‐slip events in a physical system are useful to expand the set of credible hypotheses regarding possible behavior modes of earthquake faults.

A Long‐Term Seismic Quiescence before the 2004 Sumatra (Mw 9.1) Earthquake

The 2004 Sumatra ( M w 9.1) earthquake was preceded by a seismic quiescence that began 13 years before the mainshock. An earthquake catalog created by the International Seismological Centre is analyzed in the study area, 80°–110° E, 10° S–20° N, between 1964 and 2004, including 1153 earthquakes shallower than 100 km with body‐wave magnitude of 5.0≤ m b≤6.7. A detailed analysis of the earthquake catalog using a gridding technique (ZMAP) shows the quiescent area is located between 3° and 6° N, which covers the southeastern part of the focal area, including the rupture initiation point of the 2004 Sumatra earthquake. The observed spatial pattern of quiescence can be explained by stress perturbation due to a long‐term slow slip located on the deeper edge of the mainshock fault, which is predicted by a numerical simulation based on a laboratory‐derived friction law. Although the quiescence is not significant statistically, it may still be considered unlikely that such an anomalous quiescence would occur at almost the same time and location as other long‐term anomalies reported in the previous studies, including decreases in b ‐value and tidal triggering.

Kinematic Rupture Model and Hypocenter Relocation of the 2013 Mw 6.6 Lushan Earthquake Constrained by Strong-Motion and Teleseismic Data

Online Material: Tables of 1D velocity structure, hypocentral locations, and kinematic rupture model. On 20 April 2013, an M w 6.6 earthquake struck Lushan, Sichuan province, China (hereafter as Lushan earthquake), which caused 196 deaths and 21 missing. As another disastrous earthquake occurred on the Longmenshan fault after the 2008 M w 7.9 Wenchuan earthquake, the Lushan earthquake stimulated an extensive discussion about its seismogenesis. In particular, whether it was a large aftershock of the 2008 M w 7.9 Wenchuan earthquake has been heatedly debated (Chen et al. , 2013; Du et al. , 2013; Liu, Yi, et al. , 2013; Wang et al. , 2013; Jia et al. , 2014). Actually, after the Wenchuan earthquake, an increased seismic hazard for the southwest of the Longmenshan fault has been commonly recognized (Parsons et al. , 2008; Toda et al. , 2008). The occurrence of the Lushan earthquake seems to have confirmed this common understanding, and further attracts attention on the re‐evaluation of future seismic activities on the southwest Longmenshan fault (Chen et al. , 2013). As the basis of these discussions, the source characteristics of the Lushan earthquake need to be well understood. As a routine work for fast source earthquake information, Zhang et al. (2013) released the preliminary teleseismic rupture model about three hours after the Lushan earthquake. Their results show that the earthquake has no dominant rupture direction. The major slip area is located around the hypocenter and does not reach the surface. It is known, however, that teleseismic data can only constrain the ruptured area relatively to the hypocenter (rupture initiation point). In contrast, near‐field strong‐motion data can provide information useful in precisely and accurately locating …

Estimation of Strong Ground Motion from a Great Earthquake Mw 8.5 in Central Seismic Gap Region, Himalaya (India) Using Empirical Green’s Function Technique

In the present study ground motions for a Mw 8.5 scenario earthquake are estimated at 13 sites in Kumaun-Garhwal region using the empirical Green’s function technique. The recordings of 1991 Uttarkashi earthquake of Mw 6.8 at these sites are used as an element earthquake. A heterogeneous source model consisting of two asperities is considered for simulating the ground motions. The entire central seismic gap (CSG) can expect acceleration in excess of 100 cm/s2 with NW portion in excess of 400 cm/s2 and SE between 100 and 200 cm/s2. The central portion can expect peak ground acceleration (PGA) between 200 and 400 cm/s2. It has been observed from simulation of strong ground motion that sites located near the rupture initiation point can expect accelerations in excess of 1g. In the present analysis, Bhatwari and Uttarkashi can expect ground accelerations in excess of 1g. The estimates of the PGA are compared with earlier studies in the same region using different methodologies and it was found that the results are comparable. This has put constrains on the expected PGAs in this region. The obtained PGA values can be used in identifying the vulnerable areas in the central Himalaya, thereby facilitating the planning, design and construction of new structures and strengthening of the existing structures in the region.

Fault extent of the largest aftershock of the 1968 Tokachi-Oki, Japan, earthquake and an interpretation of the normal faulting focal mechanism

The focal mechanism of the 1968 Tokachi-Oki earthquake (MJ = 7.9) was thrust faulting but that of the largest aftershock (MJ = 7.5) was normal faulting. The tectonic implication of the reversal of the focal mechanisms of the two events has not been clarified yet. In order to investigate this, we ought to take into account the relative location of the two fault planes. In the present study, the length and the direction of rupture propagation for the largest aftershock is derived from the azimuth dependence of the duration of observed strong ground motion. If we assume that the rupture initiation point is the hypocenter location determined by the Japan Meteorological Agency (JMA), the location of the fault plane is considerably further north of the tsunami source area as estimated previously, and at the northern end of the aftershock area within 24 hours after the main shock. The fault plane of the largest aftershock is deeper than that of the main shock and the two fault planes are nearly parallel to each other. The thrust faulting of the main shock and the normal faulting of the largest aftershock indicate that the part of the Pacific plate between the two fault planes moved relatively further northwestward due to the two events than the deeper part beneath the fault plane of the largest aftershock.

A Characteristic Rupture Model for the 2001 Geiyo, Japan, Earthquake

In this study we present a characteristic kinematic rupture model for an intraslab earthquake of the type of the 2001 Geiyo earthquake. The procedure for developing the characteristic rupture model follows the recipe developed by Irikura and Miyake (Proceedings of the 8th US National Conference on Earthquake Engineering, San Francisco, 2006) with a few modifications. We used the functional form of Nakamura and Miyatake [Zisin (J Seism Soc Jpn), 53, 1–9, 2000] to model the spatial and temporal variability of the slip rate function. In our procedure the earthquake source is specified by the kinematic description of the fault model that incorporates spatial heterogeneity in slip and rise time and constant rupture velocity. In the proposed characteristic model the asperity locations and rupture initiation point were the only parameters that were constrained by the available earthquake rupture models of the target earthquake. The quality of the characteristic rupture model was assessed by comparing recorded and synthetic ground motion time histories from the 2001 Geiyo earthquake calculated with a standard broadband (0.1–10 Hz) ground motion simulation technique. Our analyses show that the characteristic rupture model performs well in reproducing the recorded ground motion, in spite of its simple representation of the fault geometry and kinematic rupture complexity. The analyses of ground motion sensitivity to relative location of asperities, and their stress drop contrast suggest that the overall ground motion goodness of fit remains the same at short periods, but decreases slightly at periods longer than 1 s. We suspect that, due to the depth of the intraslab source (40–50 km), the higher-frequency ground motions are relatively insensitive to the details of the slip distribution and slip contrast. On the other hand, even for intraslab events, the lower-frequency motions are influenced by rupture directivity effects and slip distribution.

Character of slip and stress due to interaction between fault segments along the dip direction of a subduction zone

Abstract We have performed a two-dimensional numerical simulation to elucidate the physical processes governing earthquake behavior when significant stress perturbations are produced by interaction between fault segments. Our model involves two seismogenic segments separated down-dip on a subduction zone plate boundary and incorporates a rate- and state-dependent friction law. Based on repeated simulations under different scenarios, we find that the rate- and state-dependent frictional parameters (b–a) and dc in the deeper seismogenic segment are required to be smaller than those in the shallower segment in order that more deep earthquakes occur than shallow ones. Our simulations show that slip amounts in either seismogenic segment increase in each of the co-, pre- and post-seismic stages when an earthquake occurs shortly after another earthquake in the other seismogenic segment. Conversely, when earthquakes occur in a single seismogenic segment several times in succession while the other segment remains locked, all three pre-, co-, and post-seismic slip amounts become smaller. These results imply that precursory changes do not necessarily occur at the same level on every occasion. In cases of multiple rupturing, the co-seismic slip of the later earthquake in a pair is approximately characteristic when frictional stability in the aseismic segment between the two seismogenic fault segments is strong enough to produce different rates of seismicity on each segment. Our simulation also shows that the degree to which rupture initiation points vary between different earthquakes is higher in low seismic coupling regions. This result may prove useful in estimating seismic coupling coefficients from observations of interplate hypocenters.

Spatio-temporal rupture process of the 2008 great Wenchuan earthquake

Focal mechanism and dynamic rupture process of the Wenchaun M s8.0 earthquake in Sichuan province on 12 May 2008 were obtained by inverting long period seismic data from the Global Seismic Network (GSN), and characteristics of the co-seismic displacement field near the fault were quantitatively ana-lyzed based on the inverted results to investigate the mechanism causing disaster. A finite fault model with given focal mechanism and vertical components of the long period P-waves from 21 stations with evenly azimuthal coverage were adopted in the inversion. From the inverted results as well as after-shock distribution, the causative fault of the great Wenchuan earthquake was confirmed to be a fault of strike 225°/dip 39°/rake 120°, indicating that the earthquake was mainly a thrust event with right-lateral strike-slip component. The released scalar seismic moment was estimated to be about 9.4×1020―2.0×1021 Nm, yielding moment magnitude of M w7.9―8.1. The great Wenchuan earthquake occurred on a fault more than 300 km long, and had a complicated rupture process of about 90 s duration time. The slip distribution was highly inhomogeneous with the average slip of about 2.4 m. Four slip-patches broke the ground surface. Two of them were underneath the regions of Wenchuan-Yingxiu and Beichuan, respectively, with the first being around the hypocenter (rupture initiation point), where the largest slip was about 7.3 m, and the second being underneath Beichuan and extending to Pingwu, where the largest slip was about 5.6 m. The other two slip-patches had smaller sizes, one having the maximum slip of 1.8 m and lying underneath the north of Kangding, and the other having the maximum slip of 0.7 m and lying underneath the northeast of Qingchuan. Average and maximum stress drops over the whole fault plane were estimated to be 18 MPa and 53 MPa, respectively. In addition, the co-seismic displacement field near the fault was analyzed. The results indicate that the features of the co-seismic displacement field were coincident with those of the intensity distribution in the meizo-seismal area, implying that the large-scale, large-amplitude and surface-broken thrust dislocation should be responsible for the serious disaster in the near fault area.

PreSEIS: A Neural Network-Based Approach to Earthquake Early Warning for Finite Faults

The major challenge in the development of earthquake early warning (EEW) systems is the achievement of a robust performance at largest possible warning time. We have developed a new method for EEW—called PreSEIS (Pre-SEISmic)—that is as quick as methods that are based on single station observations and, at the same time, shows a higher robustness than most other approaches. At regular timesteps after the triggering of the first EEW sensor, PreSEIS estimates the most likely source parameters of an earthquake using the available information on ground motions at different sensors in a seismic network. The approach is based on two-layer feed-forward neural networks to estimate the earthquake hypocenter location, its moment magnitude, and the expansion of the evolving seismic rupture. When applied to the Istanbul Earthquake Rapid Response and Early Warning System (IERREWS), PreSEIS estimates the moment magnitudes of 280 simulated finite faults scenarios (4.5≤M≤7.5) with errors of less than ±0.8 units after 0.5 sec, ±0.5 units after 7.5 sec, and ±0.3 units after 15.0 sec. In the same time intervals, the mean location errors can be reduced from 10 km over 6 km to less than 5 km, respectively. Our analyses show that the uncertainties of the estimated parameters (and thus of the warnings) decrease with time. This reveals a trade-off between the reliability of the warning on the one hand, and the remaining warning time on the other hand. Moreover, the ongoing update of predictions with time allows PreSEIS to handle complex ruptures, in which the largest fault slips do not occur close to the point of rupture initiation. The estimated expansions of the seismic ruptures lead to a clear enhancement of alert maps, which visualize the level and distribution of likely ground shaking in the affected region seconds before seismic waves will arrive.

Frequency-domain array technique analysis for the rupture duration time and geometrical characteristics of the 2001 Kunlun Mountain Pass earthquake

In this paper, we briefly describe the principle of tracking energy radiation sources of large earthquakes using frequency-domain far-field array technique, present general steps of tracking energy radiation sources, and take the 2001 Kunlun Mountain Pass earthquake as an example to analyze key factors for setting parameters while processing data. Using broadband waveform data from a seismic array in Ethiopia and Kenya (EK Array), we obtain that the rupture initiation point of the 2001 Kunlun Mountain Pass earthquake is located in the east of Buka Daban Peak (35.92°N, 91.70°E), and the rupture duration time is less than 160 s, the rupture length about 520 km, with 180 km in the west of the initiation point and 340 km in the east, respectively. The western segment of the earthquake fault bends towards southwest near Buka Daban Peak, which is in concordance with the surface rupture trace. The eastern segment apparently bends towards northeast near Xidatan, which is in agreement with the strike of Xidatan fault, but 30 km away from Xidatan fault. In addition, the results imply that the western segment of the earthquake fault appears erect while the eastern segment appears to be gradually dipping southwards.

How Frictional Properties Lead to Either Rupture-Front Focusing or Cracklike Behavior

Abstract A numerical simulation of the stress concentration and earthquake rupture process of a circular asperity is performed using a laboratory-derived rate- and state-dependent friction law. The asperity is locked during an interseismic period, and it is surrounded by regions of stable sliding. This situation is thought to be common at plate interfaces with relatively low seismic coupling. Aseismic sliding penetrates into the asperity, and the distance of its penetration depends on frictional properties. Shear stress is concentrated in the boundary regions between the locked and stable sliding regions before earthquake occurrence, and this stress distribution affects the earthquake rupture process. When aseismic sliding propagates little into the asperity, rupture propagates faster in the stress concentrated region, and rupture fronts propagating clockwise and counterclockwise around the asperity meet at an end of the asperity opposite to the rupture initiation point. This rupture-front focusing produces high slip rates in the final stage of asperity rupture, which is consistent with observations of short-period seismic waves radiated from some large interplate earthquakes. On the other hand, when the distance that aseismic sliding propagates into the asperity is long, rupture starts near the center of the asperity and propagates outward like an expanding crack, generating no rupture-front focusing.

Temperature distribution of the upper surface of the subducted Philippine Sea Plate along the Nankai Trough, southwest Japan, from a three-dimensional subduction model: relation to large interplate and low-frequency earthquakes

The Nankai subduction fault in southwest Japan is a plate boundary along which large megathrust earthquakes have repeatedly occurred. A previous 2-D thermal model suggested that the updip and downdip limits of the seismogenic zone are closely related to the temperature of the plate interface. We estimated a new temperature distribution for the plate interface based on a 3-D thermal convection model that incorporates revised governing equations, temporal changes in relative plate motion, the shape of the subducted slab, temperature variations related to basin evolution and more heat flow data and model regions than have been used in previous models. The margin-parallel spatial variation in the temperature of the plate interface was caused by spatio-temporal changes associated with the cooling of the Shikoku Basin. The updip limit of the thermally delineated seismogenic zone (thermal seismogenic zone) was approximately parallel to the trough axis due to a spreading rate that increased with distance from a fossil ridge, although the margin-parallel age dependency of the subducting plate was taken into account. The downdip limit of the thermal seismogenic zone was determined by temperature, except in eastern Kyushu, where it was determined by a boundary between the continental Moho depth and the upper surface of the subducting plate. The maximum coseismic slip associated with the 1944 Tonankai (M 7.9) and the 1946 Nankai (M 8.0) earthquakes, and a strongly coupled region estimated from GPS data inversion obtained by previous studies, were both located in the thermal seismogenic zone on the plate interface. Low-frequency earthquakes located at the downdip of the thermal seismogenic zone took place at temperatures of about 400–500 °C. This may be related to the phase transformation of hydrous minerals in oceanic crust from lawsonite + blueschist + jadeite to amphibole + eclogite and the associated decreases in water content of approximately 2.4 wt%. The thermal seismogenic zone is narrowest off the Kii Peninsula, where the hypocentres of the Tonankai and Nankai earthquakes were located. The narrow seismogenic zone may have determined the rupture initiation points for these earthquakes, as was previously demonstrated by numerical simulations of the earthquake cycle.

Sensitivity of Ground-Motion Simulations to Earthquake Source Parameters: A Case Study for Istanbul, Turkey

Following the disastrous earthquakes in Izmit and Duzce along the North Anatolian fault in 1999, the earthquake hazard in the Istanbul area became a great concern. In this study we simulate strong ground motions caused by a scenario earthquake (M 7.5) in the Marmara Sea, and investigate the effect of varying the input parameters on the broadband frequency ground motion. Simulations are based on a multiasperity source model that involves the combined rupture of the North Anatolian fault segments beneath the Marmara Sea. We use a hybrid model combin- ing a deterministic simulation of the low frequencies (0.1-1.0 Hz) with a semisto- chastic simulation of the high frequencies (1.0-10.0 Hz). Computation at each fre- quency range is performed separately and the total ground motion is combined in the time domain. Computations are linear and are performed at bedrock level, thereby not taking any effect of local geological conditions into account. We calculate a total of 17 earthquake scenarios corresponding to different source and attenuation param- eters to study their effect on the ground motion. The most significant parameters in terms of ground-shaking level are the rise time, rupture velocity, rupture initiation point, and stress drop. The largest variability of strong ground motions is observed in regions adjacent to asperities and is associated with frequencies higher than 5 Hz. For lower frequencies our simulated velocity spectra within the Istanbul area are fairly stable among scenarios. The average standard deviations of all ground-motion measures are less than 35% of the mean. Online material: Figures of peak ground acceleration and peak ground velocity and their differences to the reference scenario values.

Self-Healing Pulse-Like Shear Ruptures in the Laboratory

Models predict that dynamic shear ruptures during earthquake faulting occur as either sliding cracks, where a large section of the interface slides behind a fast-moving rupture front, or self-healing slip pulses, where the fault relocks shortly behind the rupture front. We report experimental visualizations of crack-like, pulse-like, and mixed rupture modes propagating along frictionally held, "incoherent" interfaces separating identical solids, and we describe the conditions under which those modes develop. A combination of simultaneously performed measurements via dynamic photoelasticity and laser interferometry reveals the rupture mode type, the exact point of rupture initiation, the sliding velocity history, and the rupture propagation speed.

The rupture process during the 1999 Düzce, Turkey, earthquake from joint inversion of teleseismic and strong-motion data

Teleseismic and strong-motion data are inverted to determine the rupture process during the November 1999 Düzce earthquake in NW Turkey. The fault geometry, rise time and rupture velocity are determined from the aftershock distribution and preliminary inversions of the teleseismic data. Joint inversion of the teleseismic and strong-motion data is then carried out for the slip distribution. We obtain the strike 264°, dip 64°, rake −172°, seismic moment 5.0×10 19 N m (M w 7.1), and average stress drop 7 MPa. This earthquake was characterized by bilateral fault rupture and asymmetric slip distribution. Two asperities (areas of large slip) are identified, the eastern one being 1.5 times larger than the western one. The derived slip distribution is consistent with the aftershock distribution, surface rupture and damage. The point of rupture initiation in this Düzce earthquake coincided with the eastern tip of the aftershock distribution of the August 1999 Izmit earthquake.

SEISIMPACT-THES: A SCENARIO EARTHQUAKE AFFECTING THE BUILT ENVIRONMENT OF THE PREFECTURE OF THESSALONIKI

In the framework of the "SEISIMPACT-THES" project (Koutoupes et al., 2004; Savvaidis et al., 2004) a GIS database has been designed to include information on a wide range of components related to seismic risk within the broader area of the prefecture of Thessaloniki. One of these components refers to the distribution of strong ground motion produced by large earthquakes and the ability of a potential future user of the database to retrieve information regarding the distribution of strong ground motion from past destructive earthquakes in the area of Thessaloniki, as well as relative information for realistic future scenario earthquakes in the same area. The selection of future scenario earthquakes that may affect this urban region of interest is based on a combined review of historical data, previous probabilistic and deterministic hazard assessments, seismotectonic and microseismicity studies, relocated seismicity in northern Greece and the experience gained from worldwide research. In this study we present the results from hypothetical rupture of one fault that is located at the suburbs of the city, the Asvestochori fault. Empirical relations applicable to Greece (Papazachos & Papazachou 2003), as well as seismicity information are combined to determine the dimensions of the scenario earthquake source. Strong ground motion for the selected scenario is simulated using the stochastic method for finite faults (Beresnev and Atkinson, 1997). Uncertainties due to unknown parameters such as the rupture initiation point and the distribution of slip on the fault plane are taken into account by examining a large number of random scenarios. The average values from these multiple scenarios are then used to compile maps of strong ground motion parameters (e.g. peak ground acceleration and spectral acceleration). Although the examined scenario earthquake is moderate in size (Mw 5.2), the level of the resulting strong ground motion parameters is indicative of the potential destructiveness of the examined source. Due to the simplicity in the underlying assumptions of the stochastic method, the results of this study are a first-order approximation to the problem of defining expected shaking in the wider area of Thessaloniki. Other strong motion simulation methods of more deterministic character will also be applied for the same purpose in the framework of the SEISIMPACT-THES project.