Large Earthquake Events Research Articles

On the effectiveness of rotational friction hinge damper to control responses of multi-span simply supported bridge to non-uniform ground motions

Base isolation techniques have been extensively used to improve the seismic performance of the bridge structures. The decoupling of the bridge decks from the piers and abutments using rubber isolator could result in significant reduction in seismic forces transmitted to the bridge substructures. However, the isolation devices could also increase the deck displacement and thus enhance the possibility of pounding and unseating damage of bridge decks. Moreover, previous investigations have shown that pounding and unseating damages on isolated bridges exacerbate due to the spatial variation in earthquake ground motions. Recent earthquakes revealed that isolation bearing could also be damaged due to the excessive movements of decks during large earthquake events. This study proposes the use of rotational friction hinge dampers to mitigate the damages that could be induced by large displacement of bridge decks, particularly focusing on pounding and unseating damages and bearing damages. The device is capable of providing large hysteretic damping and the cost of installing the devices is relatively economical. This article presents numerical investigations on the effectiveness of these devices on a typical Nepalese simply supported bridge subjected to spatially varying ground motions. The results indicate that rotational friction hinge dampers are very effective in mitigating the relative displacement and pounding force, as well as controlling the bearing deformation and pier drift. It is also revealed that the effectiveness of the device is not significantly affected by small changes in the slip forces; thus, small variations in the optimum slip forces during the lifetime of the bridge do not warrant any adjustment or replacement of the device.

Correlating damage condition with historical seismic activity in underground sepulchral monuments of Cyprus

Severe and repeated earthquakes devastated Cyprus in antiquity, causing in many cases the abandonment of entire settlement sites. Yet, information regarding the level of seismic activity of historical seismicity in Cyprus is very limited and does not provide the evidence to arrive at reliable conclusions relative to hazard damage parameters such as the severity or occurrence frequency of a seismic event. Thereafter, the level of risk in which these monuments are exposed is unclear leading to an increased uncertainty regarding their safeguarding from future events.The paper aims at investigating the correlation between damage observed in underground ancient tombs and the historical seismic activity at the area based on in situ observations and expert opinion analysis. In addition, the paper aims to simulate the current state of the tomb's structure, and predict, through a seismic scenario, the propagation of damage from future large earthquake events. Underground monuments are chosen since, due to the nature of the seismic force, they are further “protected” and capable of surviving strong ground motions as they follow the displacement of the soil surrounding them. Typical examples of such structures in Cyprus are the hypogea in the necropolis of the “Tombs of the Kings”, located in Paphos area. Some of these monuments exhibit severe cracking of the rock-cut stone walls and evidence of collapse of vertical resisting members of skeleton structure. Paphos area is the most active seismic region in Cyprus based on the historical catalogue of events with evidence of a number of destructive earthquakes.The framework presented herein utilizes information regarding the current geometry of these structures as documented from topographical surveys, their depth, area of opening, size of resisting members along with information regarding the geotechnical conditions at the site to arrive at estimates of the displacement demand under various seismic scenarios. The predicted shear strain levels on the walls are compared with the strain capacity under tension of the soil material to identify the possibility of propagation of cracking of the walls based on a specific seismic scenario.

Piezomagnetic In-situ Stress Monitoring and its Application in the Longmenshan Fault Zone

The relative change of in-situ stress is an inevitable outcome of differential movement among the crust plates. Conversely, changes of in-situ stress can also lead to deformation and instability of crustal rock mass, trigger activity of faults, and induce earthquakes. Hence, monitoring real-time change of in-situ stress is of great significance. Piezomagnetic in-situ stress monitoring has good and longtime applications in large engineering constructions and geoscience study fields in China. In this paper, the new piezomagnetic in-situ stress monitoring system is introduced and it not only has overall improvements in measuring cell's structure and property, stressing and orienting way, but also enhances integration and intelligence of control and data transmission system, in general, which greatly promotes installing efficiency of measuring probe and quality of monitoring data. This paper also discusses the responses of new piezomagnetic system in large earthquake events of in-situ stress monitoring station at Qiaoqi of Baoxing and Wenxian of Gansu. The monitoring data reflect adjustments and changes of tectonic stress field at the southwestern segment of and the northern area near the Longmenshan fault zone, which shows that the new system has a good performance and application prospect in the geoscience field. Data of the Qiaoqi stress-monitoring station manifest that the Lushan Earthquake did not release stress of the southwestern segment of the Longmenshan fault zone adequately and there still probably exists seismic risk in this region in the future. Combined with absolute in-situ stress measurement, carrying out long-term in-situ stress monitoring in typical tectonic position of important regions is of great importance for researchers to assess and study regional crust stability.

Large Earthquake Occurrence Estimation Based on Radial Basis Function Neural Networks

This paper presents a novel scheme for the estimation of large earthquake event occurrence based on radial basis function (RBF) neural network (NN) models. The input vector to the network is composed of different seismicity rates between main events, which are easy to calculate in a reliable manner. Training of the NNs is performed using the powerful fuzzy means training algorithm, which, in this case, is modified to incorporate a leave-one-out training procedure. This helps the algorithm to account for the limited number of training data, which is a common problem when trying to model earthquakes with data-driven techniques. Additionally, the proposed training algorithm is combined with the Reasenberg clustering technique, which is used to remove aftershock events from the catalog prior to processing the data with the NN. In order to evaluate the performance of the resulting framework, the method is applied on the California earthquake catalog. The results show that the produced RBF model can successfully estimate interevent times between significant seismic events, thus resulting to a predictive tool for earthquake occurrence. A comparison with a different NN architecture, namely, multilayer perceptron networks, highlights the superiority of the proposed approach.

Piezoelectric dynamic strain monitoring for detecting local seismic damage in steel buildings

This research presents a methodology for damage detection along with a sensing system for monitoring seismic damage in steel buildings. The system extracts the location and extent of local damage, such as fracture at a beam–column connection, from changes in the bending moment distribution in a steel moment-resisting frame. We developed a dynamic strain-based sensing system utilizing piezoelectric film sensors and wireless sensing techniques to estimate the bending moments resisted by individual structural members under small amplitude loadings such as ambient vibrations and minor earthquakes. We introduce a new damage index that extracts local damage information from the comparative study of the dynamic strain responses of the structural members before and after a large earthquake event. The damage detection scheme was examined both analytically and numerically using a simple frame example. Then, the entire local damage detection scheme was verified through a series of vibration tests using a one-quarter-scale steel testbed that simulated seismic damage at member ends.

Strategy for separation and treatment of disaster waste: a manual for earthquake and tsunami disaster waste management in Japan

Shortly after the March 11th earthquake and tsunami in eastern Japan, a Task Team for Disaster Waste Management and Reconstruction was established within the Japan Society of Material Cycles and Waste Management (JSMCWM). One of the major tasks undertaken by the team was to create a manual entitled, Strategies for Separation and Treatment of Disaster Waste. In this paper, this JSMCWM manual is introduced, followed by a review of existing guidelines for disaster waste management in various countries. We identify useful guidelines created by international agencies, national and local governments. The JSMCWM manual adds our new experiences, especially characterized by a huge scale of disaster and tsunami information, to the existing knowledge with an emphasis on separation and subsequent treatment options. It should be desirable to share our knowledge and experiences, not only domestically but also with other countries in the world, especially regions that could be affected by large earthquake and tsunami events.

Interevent times in a new alarm-based earthquake forecasting model

SUMMARY This study introduces a new earthquake forecasting model that uses the moment ratio (MR) of thefirst to second order moments of earthquake interevent times as a precursory alarm index to forecast large earthquake events. This MR model is based on the idea that the MR is associated with anomalous long-term changes in background seismicity prior to large earthquake events. In a given region, the MR statistic is defined as the inverse of the index of dispersion or Fano factor, with MR values (or scores) providing a biased estimate of the relative regional frequency of background events, here termed the background fraction. To test the forecasting performanceofthisproposedMRmodel,acompositeJapan-wideearthquakecatalogueforthe years between 679 and 2012 was compiled using the Japan Meteorological Agency catalogue for the period between 1923 and 2012, and the Utsu historical seismicity records between 679 and 1922. MR values were estimated by sampling interevent times from events with magnitude M ≥ 6 using an earthquake random sampling (ERS) algorithm developed during previous research. Three retrospective tests of M ≥ 7 target earthquakes were undertaken to evaluate the long-, intermediate- and short-term performance of MR forecasting, using mainly Molchan diagrams and optimal spatial maps obtained by minimizing forecasting error defined by miss and alarm rate addition. This testing indicates that the MR forecasting technique performs well at long-, intermediate- and short-term. The MR maps produced during longterm testing indicate significant alarm levels before 15 of the 18 shallow earthquakes within the testing region during the past two decades, with an alarm region covering about 20percent (alarm rate) of the testing region. The number of shallow events missed by forecasting was reduced by about 60percent after using the MR method instead of the relative intensity (RI) forecasting method. At short term, our model succeeded in forecasting the occurrence region of the 2011 Mw 9.0 Tohoku earthquake, whereas the RI method did not. Cases where a period of quiescent seismicity occurred before the target event often lead to low MR scores, meaning that the target event was not predicted and indicating that our model could be further improved by taking into account quiescent periods in the alarm strategy.

Seismic Hazard Analysis for Kuala Lumpur, Malaysia

In the past, probabilistic seismic hazard analysis (PSHA) has been performed by researchers to assess the level of seismic hazard in Kuala Lumpur, Malaysia and its vicinity. However, the peak ground acceleration (PGA) values obtained are high due to unsuitable ground motion prediction equation (GMPE). This article is divided into two parts: development of a suitable GMPE and the PSHA for this region. Two main sources have been identified as the contributors to earthquake hazard in Peninsular Malaysia, namely the Sumatra strike-slip fault and Sumatra subduction zone. For the subduction zone, nine recorded large earthquake events are analyzed and regression analysis is performed to obtain a new GMPE for this region. In performing PSHA, the strike-slip fault is divided into 14 zones based on the individual fault segments, while the subduction is divided into 4 zones. Historical earthquakes of this region are collected, processed, and segregated according to the zones. PSHA has been conducted by modeling the source seismicity using Gutenberg-Richter and characteristic earthquake models. The developed GMPE has been used along with other attenuation models: Megawati and Pan [2010] and component attenuation model (CAM) by Balendra et al. [2002] for subduction; and Sadigh et al. [1997] and CAM for strike-slip fault. The peak ground accelerations in Kuala Lumpur for 10% and 2% probability of exceedances in 50 years are found to be 16.5 gal and 23.4 gal, respectively. From deaggregation analysis, the main contributor for the 10% probability of exceedance in 50 years is found to be a 7.5 Mw earthquake at 300 km, originating from the strike slip fault. Finally, the design response spectrum for Kuala Lumpur is developed for rock sites, which would be amplified further by local soil profile.

A case study of the association of total ozone variability with major earthquakes in Greece during 2001–2010

Recent studies have suggested that variation of the total ozone content may be a precursor tool for earthquake forecasts. The main aim of this analysis is to examine whether the total ozone variability before and after the eight large earthquakes (M w ≥ 6.0) of the decade 2001–2010 in Greece could be related with these earthquake events. The results clearly show that the association of total ozone fluctuation with earthquake occurrence in the time window of 2 weeks before and after each of these large earthquake events is not statistically significant.

Performance assessment of low–rise confined masonry structures for Earthquake induced ground motions

The performance of low-rise confined masonry (unreinforced masonry walls confined with horizontal and vertical lightly reinforced concrete elements) structures is assessed against earthquake induced site amplified strong ground motions using a probabilistic-based approach. This included analytical investigation of field representative structural models through a suite of natural accelerograms, for various hazard levels. The basic mechanical characteristics of structural material is obtained through experimental investigations recently carried out on masonry material, structural walls and reduced scale structural models, which are employed for the design, mathematical modeling and seismic analysis of confine masonry structures. The seismic performance of two case study (two storey) structure types is assessed for various scenario earthquakes with moderate to strong ground motions. The structures are designed and analyzed considering the existing building stock and new construction recommendations; both differ in provisioning of basic mechanical properties of building material for construction. The typical confinement of masonry walls can avoid the total structural collapse in most of the strong ground motions thereby minimizing the occupant's injuries, however the damages to structures in large earthquake events are significant. Besides the good behavior offered by confinement scheme, the role of construction material's mechanical properties in performance improvement is significant.

Near-Fault Directivity Spectrum for Nuclear Structure Design on Rock Site

This study is aimed at evaluating the safety implications of near-fault directivity effect on nuclear structure and facilities designed according to the Chinese code. To this end, a set of near-fault ground motions at rock site with typical forward-directivity effect is examined with emphasis on several key parameters and response spectra. The bi-normalized response spectra in terms of different corner periods are utilized to derive nuclear design spectra. It was concluded that nuclear design spectra on rock site derived from typical directivity records are significantly influenced by both magnitude and distance. The nuclear design spectra specified in the code need to be adjusted to reflect the near-fault directivity effect of large earthquakes.

The present-day seismicity variations in the Kuril-Kamchatka seismic zone

This study is concerned with seismicity variations in Kamchatka and the Kuril Islands for the period 1962–2009; the effects of large earthquakes on the seismicity of adjacent areas are taken into account. The 1997 Kronotskii earthquake was followed by seismicity decreases in most areas over Kamchatka, which is presumably related to decreased tectonic stresses. After the 2007 Simushir earthquake synchronization and periodicities in seismicity were identified, indicating increased instabilities and the likelihood of a large event in Kamchatka in the near future. The instability of seismic regions is discussed within the framework of the theory of nonequilibrium dynamical systems. We suggest successive phases in the occurrence of seismological precursors.

Response spectra for nuclear structures on rock sites considering the near-fault directivity effect

Near-fault ground motions, potentially with large amplitude and typical velocity pulses, may significantly impact the performance of a wide range of structures. The current study is aimed at evaluating the safety implications of the near-fault effect on nuclear power plant facilities designed according to the Chinese code. To this end, a set of nearfault ground motions at rock sites with typical forward-directivity effect is examined with special emphasis on several key parameters and response spectra. Spectral comparison of the selected records with the Chinese and other code design spectra was conducted. The bi-normalized response spectra in terms of different corner periods are utilized to derive nuclear design spectra. It is concluded that nuclear design spectra on rock sites derived from typical rupture directivity records are significantly influenced both by the earthquake magnitude and the rupture distance. The nuclear design spectra specified in the code needs to be adjusted to reflect the near-fault directivity effect of large earthquakes.

Dip-slip rate determined by cosmogenic surface dating on a Holocene scarp of the Daju fault, Yunnan, China

The Daju and Lijiang-Daju fault zones which bound the Yulong Mountains on its northern and eastern perimeters, respectively, are segments of a continuous fault system that bends at Daju. Uplift of the Yulong Mountains, the southernmost glacierized mountain range in Eurasia, resulted from the normal faulting characteristics of the fault system. Using cosmogenic surface exposure dating with 10Be and 26Al, we have measured bedrock exposure ages as a function of elevation along an exposed bedrock scarp of the Daju fault. 10Be and 26Al exposure ages increase monotonically with elevation ranging from 2.6 to 9.6 ka over the 51 m scarp length giving an average dip-slip rate of 7.5 m/ka during the Holocene period and a vertical uplift rate of 5.7 m/ka. The 5.7 m/ka Holocene uplift rate and supporting geomorphic features suggest that the uplift of the Yulong Mountains mainly occurred in the Quaternary. The fast slip rate and seismic quiescence for the recent 2.8 ka call attention to the possible recurrence of large magnitude earthquake events along the fault zone.

Trenching exposures of the surface rupture of 2008 Mw 7.9 Wenchuan earthquake, China: Implications for coseismic deformation and paleoseismology along the Central Longmen Shan thrust fault

The May 12, 2008, Mw 7.9 Wenchuan earthquake was induced by failure of two of the major faults of the Longmen Shan thrust fault zone along the eastern margin of Tibet Plateau. Our study focused on trenches across the Yingxiu–Bichuan fault, the central fault in the Longmen Shan belt that has a coseismic surface break of more than 200 km long. Trenching excavation across the 2008 earthquake rupture on three representative sites reveals the styles and amounts of the deformation and paleoseismicity along the Longmen Shan fault. Styles of coseismic deformation along the 2008 earthquake rupture at these three sites represent three models of deformation along a thrust fault. Two of the three trench exposures reveal one pre-2008 earthquake event, which is coincident with the pre-existing scarps. Based on the observation of exposed stratigraphy and structures in the trenches and the geomorphic expressions on ground surface, we interpret the 2008 earthquake as a characteristic earthquake along this fault. The interval of reoccurrence of large earthquake events on the Central Longmen Shan fault (the Yingxiu–Beichuan fault) can be inferred to be about 11,000 years according to 14C and OSL dating. The amounts of the vertical displacement and shortening across the surface rupture during the 2008 earthquake are determined to be 1.0–2.8 m and 0.15–1.32 m, respectively. The shortening rate and uplift rate are then estimated to be 0.09–0.12 mm/yr and 0.18–0.2 mm/yr, respectively. It is indicated that the deformation is absorbed mainly not by shortening, but by uplift along the rupture during the 2008 earthquake.

Noise to signal: A microtremor study at liquefaction sites in the New Madrid Seismic Zone

Understanding how sedimentary basins respond to seismic-wave energy generated by large earthquake events is a significant concern for seismic-hazard estimation. This study explores the use of microtremors, or ambient noise, for evaluating strong-motion site effects. The study focuses on the Mississippi Embayment in the New Madrid Seismic Zone, where widespread liquefaction and ground failure occurred during the 1811–1812 earthquake sequence. Spectral analyses of microtremor data at sites representing different environments of deposition (and sedimentary facies), different embayment thicknesses, and varying liquefaction susceptibility show correlations between (1) calculated vulnerability indices and evidence of liquefaction, (2) sediment thickness and fundamental resonant frequency, and (3) subsurface stratigraphic boundaries and observed peaks in horizontal-to-vertical spectral ratios. Results of the study suggest that the microtremor method could be helpful in identifying those areas most vulnerable to ground amplification in intraplate sedimentary basins, where large earthquakes are infrequent but potentially damaging.

Stable isotope constraints on vein formation and fluid evolution along a recent thrust fault in the Cascadia accretionary wedge

In situ secondary ionization mass spectrometry (SIMS) analyses of oxygen isotopes in authigenic calcite veins were obtained from an active thrust fault system drilled at Ocean Drilling Program (ODP) Site 892 (44°40.4′N, 125°07.1′W) along the Cascadia subduction margin. The average δ18OPDB value of all samples is −9.9‰ and the values are the lowest of any measured in active accretionary prisms. Ranges in individual veins can be as much as 19.6‰. There is an isotopic stratigraphy related to the structural stratigraphy. Mean isotope values in the hanging wall, thrust, and footwall are −14.4‰, −9.5‰, and −5.2‰, respectively. Several veins and crosscutting vein sequences show a general trend from lower to higher δ18O values over time. Isotopic and textural data indicate several veins formed by a crack-seal mechanism and growth into open fractures. The best explanation for the strong 18O depletions is periodic rapid flow from 2–3km deeper in the prism. Relatively narrow isotopic ranges for most veins suggest that fluids were derived from a similar source depth for each episode of fluid pulse and calcite crystallization. Structural and mass balance considerations are consistent with a record preserved in the veins of ten to hundreds of thousands of years. The fluid pulses may relate to periodic large earthquake events such as those recognized in the paleoseismicity records from the Cascadia margin.

Holocene earthquake record offshore Portugal (SW Iberia): testing turbidite paleoseismology in a slow-convergence margin

The SW margin of the Iberian Peninsula hosts the present-day boundary between the Eurasian and African Plates. Convergence (4–5 mm/yr) is accommodated through a wide deformation zone characterized by moderate magnitude seismic activity. This zone has also been the source of the most important seismic events in Western Europe, such as the 1755 Lisbon Earthquake and Tsunami and 1969 Horseshoe Earthquake. Despite efforts to identify active seismogenic structures in the Gulf of Cadiz in the last ten years, little is known about its paleoseismic history. The turbidite paleoseismology approach was applied for the first time in a low-rate convergent margin to determine the recurrence interval of large earthquake events that occurred in SW Iberia during the Holocene. Four sediment cores collected at strategically located sites offshore Portugal (i.e. Tagus Abyssal Plain, Infante Don Henrique Basin and Horseshoe Abyssal Plain) reveal that these deep-sea basins preserve a record of episodic deposition of turbidites. In the SW Iberian Margin excluding special climatic events, earthquakes are the most likely triggering mechanism for synchronous, widely-spaced distributed turbidites during the Holocene, when the sea level was relatively stable. Age correlation together with textural, mineralogical, physical properties and geochemical signatures of the new cores complemented by pre-existing multicores and gravity cores reveals a total of 7 widespread turbidite events for the Holocene. Precise dating of the most recent turbidite event (E1) based on 210Pb and 137Cs geochronology provides an age of AD 1971 ± 3. This age corresponds to a high-magnitude instrumental earthquake in the region: the 1969 Horseshoe Earthquake (Mw 8.0). Calibrated 14C ages of subsequent widespread turbidite events (E3 and E5) correlate with the dates of important historical earthquakes and paleotsunami deposits in the Gulf of Cadiz area, such as AD 1755 and 218 BC, respectively. If older synchronous events (E6, E8, and E10) with ages ranging from 4960–5510 yr BP to 8715–9015 yr BP are also taken into account, a great earthquake recurrence interval of about 1800 years is obtained for the Holocene. Our correlations suggest that the turbidite record may be considered as a proxy for paleoseismic activity in low-convergence rate margins, and a valuable complementary tool in earthquake and tsunami hazard assessment along the coasts of the Iberian Peninsula and North Africa.

Earthquake-related gravity field changes at Beijing-Tangshan gravimetric network during 1987–1998

Based on the 46 batch repeated observations of Beijing-Tangshan gravimetric network, the gravity field changes of the region during 1987–1998 have been determined. A comparison was made between the differences of these gravity field changes and the 8 reasonably large earthquake events (Mb≥ 4.0) in the region, showing the existence of the earthquake-related gravity field changes. It appears that there is usually a detectable change of a nearby gravity field well before an earthquake, followed by an opposite change afterwards.

Simulations of strong ground motion in SW Iberia for the 1969 February 28 (Ms= 8.0) and the 1755 November 1 (M∼ 8.5) earthquakes - I. Velocity model

SUMMARY This is the first paper of a series of two concerning strong ground motion in SW Iberia due to earthquakes originating from the adjacent Atlantic area. The aim of this paper is to build and calibrate a velocity model that will be used in the companion paper for seismic intensity modelling of the 1969 (M s = 8.0) and 1755 (M = 8.5‐8.7) earthquakes. Taking into account the geological evolution of the region since the Palaeozoic, we build a 3-D velocity model down to the Moho discontinuity, substantially different from a simple 1-D layered model. The velocity model presented in this paper is built a priori, using information originating from a variety of geological and geophysical studies. Its resolution is sufficient to simulate realistically seismic wave propagation in the low-frequency (f < 0.5 Hz) range, which is the most significant for the study of the destructive effects of large earthquakes at a regional scale. To validate the model, we compute synthetic seismograms for three recent earthquakes of moderate magnitudes (4.6 < M w < 5.3) located offshore, in the most seismically active area in the region. Synthetics are generated using a wave propagation code, based on the finite-difference method, which was chosen for its simplicity and accuracy in the frequency range considered in this study (0.1‐0.5 Hz). We compare simulated waveforms with threecomponent seismograms for 9 different stations. Traveltimes of the direct P waves, and the amplitude of ground motion, are accurately reproduced at all stations. The frequency content of the seismograms fits the observations, especially for the lowest frequencies investigated (0.1‐0.3 Hz). For each earthquake, the estimated seismic moment is in good agreement with values obtained by other authors, using different methods. We conclude that the velocity model provides encouraging results for the computation of low frequency seismograms in the region, and can be used for the study of larger earthquakes, for which the radiated wavefield has a predominant low-frequency spectrum.