Near-source Region Research Articles

Challenges in the definition of input motions for forensic ground-response analysis in the near-source region

This article scrutinizes the determination of input motions for forensic ground-response analysis in the near-source region, based on recorded surface ground motions at strong-motion station sites, from the same event. The first part of the article draws upon observed ground motions from the 22 February 2011 6.2 Mw Christchurch earthquake to discuss key challenges of the problem associated with the strong spatial variation of ground motion in the near-source region. Effects from the complexity of the rupture, propagation of seismic waves through complex geological structures, and site characteristics are explored. It is argued that, because of the strongly varying source-path “signature” on near-source ground motions, “reference” input motions for ground-response analysis must be specific to, and have similar signature characteristics (be “compatible”) with, the target site which is subject to the analysis. The second part of the article presents a four-step procedure for the derivation of site-specific input motions involving (1) determination of the reference layer where the input motion is to be applied in the analysis, (2) record selection considering the appropriateness of the recording station site for deconvolution and its compatibility with the target site, (3) deconvolution of the selected record to remove local site effects from the recorded ground motion, and (4) scaling of the deconvolved motion to account for differences in the source-to-site distance between the recording station and the target site. As part of the proposed procedure, a novel (amplitude-duration) scaling method is presented. Results from one-dimensional (1D) effective-stress analysis of two target Christchurch sites using input motions from the proposed procedure are used to critically evaluate the procedure and discuss essential requirements for its successful application.

The 2010 Haiti earthquake revisited: An acoustic intensity map from remote atmospheric infrasound observations

In the days following the January 12, 2010 Mw 7 Haiti earthquake the shaking intensity near the epicenter was overestimated and the spatial extent of the potentially damaging shaking was underestimated. This was due to the lack of seismometers in the near-source region at the time of the earthquake. Besides seismic waves, earthquakes generate infrasound, i.e., inaudible acoustic waves in the atmosphere. Here we show that infrasound signals, detected at distant ground-based stations, can be used to generate a map of the acoustic intensity, which is proportional to the shaking intensity. This is demonstrated with infrasound from the 2010 Haiti earthquake detected in Bermuda, over 1700 km away. Wavefront parameters are retrieved in a beamforming process and are backprojected to map the measured acoustic intensity to the source region. The backprojection process accounts for horizontal advection effects due to winds and inherent uncertainties with regard to the time of detection and the back azimuth resolution. Furthermore, we resolve the ground motion polarity in the epicentral region and use synthetics generated by an extended infrasound source model to support this result. Infrasound measurements are conducted globally for the verification of the Comprehensive Nuclear-Test-Ban Treaty and although the network was designed to provide global coverage for nuclear explosions in the atmosphere, it is shown in this paper that there is also global coverage for the estimation of acoustic shaking intensity. In this study, we lay the groundwork that can potentially make infrasound-based ShakeMaps a useful tool alongside conventional ShakeMaps and a valuable tool for earthquake disaster mitigation in sparsely monitored regions.

Assessment of viscoelasticity of ex vivo bovine cartilage using Rayleigh wave method in the near-source and far-field region

Cartilage viscoelasticity changes as cartilage degenerates. Hence, a cartilage viscoelasticity measurement could be an alternative to traditional imaging methods for osteoarthritis diagnosis. In a previous study, we confirmed the feasibility of viscoelasticity measurement in ex vivo bovine cartilage using the Lamb wave method. However, the wave speed-frequency curve of Lamb wave is totally nonlinear and the cartilage thickness could significantly affect the Lamb wave speed, making wave speed measurements and viscoelasticity inversion difficult. The objective of this study was to measure the cartilage viscoelasticity using the Rayleigh wave method (RWM). Rayleigh wave speed in the ex vivo bovine cartilage was measured, and exists only in the near-source and far-field region. The estimated cartilage elasticity was 0.66 ± 0.05 and 0.59 ± 0.07 MPa for samples 1 and 2, respectively; the estimated cartilage viscosity was 24.2 ± 0.7 and 27.1 ± 1.8 Pa·s for samples 1 and 2, respectively. These results were found to be highly reproducible, validating the feasibility of viscoelasticity measurement in ex vivo cartilage using the RWM. Current method of cartilage viscoelasticity measurement might be translated into in vivo application.

Regional broad-band ground-shaking modelling over extended and thick sedimentary basins: an example from the Lower Rhine Embayment (Germany)

The simulation of broad-band (0.1 to 10 + Hz) ground-shaking over deep and spatially extended sedimentary basins at regional scales is challenging. We evaluate the ground-shaking of a potential M 6.5 earthquake in the southern Lower Rhine Embayment, one of the most important areas of earthquake recurrence north of the Alps, close to the city of Cologne in Germany. In a first step, information from geological investigations, seismic experiments and boreholes is combined for deriving a harmonized 3D velocity and attenuation model of the sedimentary layers. Three alternative approaches are then applied and compared to evaluate the impact of the sedimentary cover on ground-motion amplification. The first approach builds on existing response spectra ground-motion models whose amplification factors empirically take into account the influence of the sedimentary layers through a standard parameterization. In the second approach, site-specific 1D amplification functions are computed from the 3D basin model. Using a random vibration theory approach, we adjust the empirical response spectra predicted for soft rock conditions by local site amplification factors: amplifications and associated ground-motions are predicted both in the Fourier and in the response spectra domain. In the third approach, hybrid physics-based ground-motion simulations are used to predict time histories for soft rock conditions which are subsequently modified using the 1D site-specific amplification functions computed in method 2. For large distances and at short periods, the differences between the three approaches become less notable due to the significant attenuation of the sedimentary layers. At intermediate and long periods, generic empirical ground-motion models provide lower levels of amplification from sedimentary soils compared to methods taking into account site-specific 1D amplification functions. In the near-source region, hybrid physics-based ground-motions models illustrate the potentially large variability of ground-motion due to finite source effects.

Non-Double-Couple Components of the Moment Tensor in a Transversely Isotropic Medium

ABSTRACTThe non-double-couple (non-DC) components of the moment tensor provide insight into the earthquake processes and anisotropy of the near-source region. We investigate the behavior of the isotropic (ISO) and compensated linear vector dipole (CLVD) components of the moment tensor for shear faulting in a transversely ISO medium with an arbitrarily oriented symmetry axis. Analytic formulas for ISO and CLVD depend on the orientation of the fault relative to the anisotropy symmetry axis as well as three anisotropic parameters, which describe deviations of the medium from isotropy. Numerical experiments are presented for the preliminary reference Earth model. Both ISO and CLVD components are zero when the axis of symmetry is within the fault plane or the auxiliary plane. For any orientation in which the ISO component is zero, the CLVD component is also zero, but the opposite is not always true (e.g., for strong anisotropy). The relative signs of the non-DC components of neighboring earthquakes may help distinguish source processes from source-region anisotropy. We prove that an inversion of ISO and CLVD components of a set of earthquakes with different focal mechanisms can uniquely determine the orientation and strength of anisotropy. This study highlights the importance of the ISO component for constraining deep slab anisotropy and demonstrates that it cannot be neglected.

DNS study of passive plume interference emitting from two parallel line sources in a turbulent channel flow

Turbulent mixing of dual plumes emitting simultaneously from line sources in a turbulent channel flow has been studied using direct numerical simulation (DNS). Three test cases have been compared to investigate the effects of the source separation on turbulent mixing of the two instantaneous plumes. The dispersion and interference of dual plumes are investigated in both physical and spectral spaces, which include an analysis of statistical moments of the concentration field, cross-correlation between the two instantaneous plumes, pre-multiplied spectra of the velocity and concentration fields, and co-spectrum and coherency spectrum of the dual plumes. As the downstream distance from the line source increases, the plume development associated with a single source emission transitions from a turbulent convective stage to a turbulent diffusive stage. It is observed that a plume released from a ground-level source reaches the turbulent diffusive stage faster than that released from an elevated source. It is also observed that a smaller separation between the two line sources tends to facilitate a more rapid growth in the cross-correlation coefficient of two instantaneous plumes. In the near-source region, the maximum coherency spectrum is produced at lower frequencies indicating that dual-plume mixing is dominated by the external flapping effects of large-scale eddy motions. However, in the far downstream region of the sources, the coherency spectrum in the higher frequency range increases significantly, indicating that the spread of the total plume is larger than all scales of turbulent eddies, such that they all contribute to the in-plume mixing of the dual plumes.

Numerical investigation on the effects of dike around liquid hydrogen source on vapor cloud dispersion

Safety is one of the most important concerns in handling liquid hydrogen. Mixture model and Realizable k-ε model are adopted to simulate the spills of liquid hydrogen in the present work. Effects of a dike around the liquid hydrogen source on vapor cloud dispersion are numerically investigated. The dike increases the hydrogen concentration near the source, and promotes the upward movement of flammable cloud thanks to the enhanced mixing with air, reducing the cloud detachment distance. The time needed for the hydrogen vapor cloud to be diluted out of hazards is largely influenced by dike size, and introducing the dike does not necessarily increase the overall hazard duration. Increasing the height to length ratio of the dike makes the near-source region exposed to high hydrogen concentration for longer hazard duration, while detachment distance reduces with the increment in dike height.

Heavy particle transport in a trellised agricultural canopy during non-row-aligned winds

Agricultural systems are exposed to and influenced by particles of many types (e.g., pathogens, pollen, pests), the concentrations of which are typically highest in the regions immediately surrounding their sources. The intermittent nature of trellised canopies creates an unique canopy architecture that directly affects the shape of particulate plumes and tends to alter their transport patterns in the near-source region. To investigate the behavior of particle plumes near their sources in a trellised canopy, a set of particle release experiments was conducted during a field campaign in an Oregon vineyard in 2013. Specifically, plumes of inert fluorescent microspheres (10–45 μm diameter) were released into the canopy during periods when the mean wind direction was significantly different from the vine-row direction. Plume concentrations were collected at over 100 separate locations in a three-dimensional space <10 canopy heights downwind of the source during each release period. These plumes were more complex than those released during periods of row-aligned winds. A novel analysis approach using the superposition of two orthogonal Gaussian plume equations was developed to quantitatively assess the behavior of the plumes’ shape and its dependence on wind direction and magnitude and on particle release height. Basic plume shape parameters, as determined by integrating the superposed Gaussian equation, varied significantly as a function of the mean wind direction. As the wind direction changed from roughly row-diagonal to directly row-normal, the rate at which the spanwise plume width increased with downwind distance increased by a factor of two. Similarly, the rate at which the plume height increased with downwind distance was higher for row-perpendicular plumes than for row-diagonal plumes. Row-diagonal plumes exhibited a much higher spanwise skewness than did the row-normal plumes, but for all plumes the skewnesses tended towards zero (symmetric) with increasing downwind distance.

Dispersion of carbon dioxide plume in street canyons

Abstract When road tankers or pipelines fail in a city, the released gas generates cloud in street canyons. The toxic heavy gas cloud pollutes the environment and harms the living being’s life. The concentration distribution and trail of the cloud are very important parameters for the emergency response. The wind tunnel experiment and the Computational Fluid Dynamics (CFD) method were applied in studying the transport and dispersion of carbon dioxide (CO2) plume, which was a typical type of heavy gas, in a long street with an intersection. The numerical simulated results using the SST k-ω model were in acceptable agreement with the experimental data. The stationary pre-release flow field in street canyons was characterized by the lee eddy generated on the sharp edges of the building top and sides. In this work, the entire releasing and dispersing process of CO2 can be divided into two stages or two regions. The motion of CO2 cloud was primarily determined by the jet speed and slightly affected by wind in near-source region. The next stage began with the collapse of CO2 cloud. The gravity and wind together influenced the concentration distribution of CO2. Both leakage rate and wind speed had significant impacts on CO2 distribution pattern within an urban street canyon.

Seismic actions on structures in the near-source region of the 2016 central Italy sequence

The central Italy seismic sequence began in the latter half of 2016 and continued well into 2017, causing severe damage in the villages close to the source and causing hundreds of casualties. It is a sequence especially interesting to study, from the perspective of seismic actions experienced by structures, because it saw nine M ≥ 5.0 earthquakes within a period of 5 months, rupturing parts of the complex central Apennine mountain range fault system. Consequently, some of the main earthquake engineering issues that arose are the multiple locations where the code-mandated seismic actions were exceeded in more than one of the main events of the sequence and the number of pre- and low-code existing buildings that suffered heavy damage or collapse due to the intensity of individual earthquakes and the cumulative effect of repeated damaging shocks. The present article picks up on these topics and uses probabilistic seismic hazard, as well as the multitude of strong ground motion recordings available from the sequence, to provide a discussion on certain issues, that are all related to the topical subject of seismic actions. These issues are: (1) the unsurprising exceedance of code spectra in the epicentral areas of strong earthquakes; (2) the particular spectral shape and damaging potential of near-source, pulse-like, ground motions, possibly related to rupture directivity; and (3) structural non-linear behaviour in the wake of a sequence that produces repeated strong shaking without the necessary respite for repair and retrofit operations.

On the evolution of the plume function and entrainment in the near-source region of lazy plumes

Plumes occur in many natural and industrial settings, such as chimney smoke, volcanic eruptions and deep water oil spills. A plume function, $\unicode[STIX]{x1D6E4}$, is used to characterize plumes and jets. The far-field behaviour of these flows has been studied in great detail while the near-field behaviour has not quite received the same attention. We examine near-field phenomena such as radial constriction, termed necking, and vortex structure formations with new high resolution direct numerical simulations. Four lazy plumes with increasing values of the source plume parameter, $\unicode[STIX]{x1D6E4}_{0}$, are simulated. We study the evolution of entrainment and the plume function. The original assumptions, that Reynolds stresses dominate viscous shear stresses, do not hold for lazy plumes in the near field. Due to this, a deviation from self-similarity occurs initially and is corrected by a large entrainment coefficient caused by vortex stretching and compression. After correcting for the virtual origin, comparison between theory and simulations shows a monotonic decay of $\unicode[STIX]{x1D6E4}$ towards pure plume behaviour. The entrainment coefficient asymptotes to a widely accepted constant value for plumes.

Peak ground accelerations from large (M\xa0\u2265\xa07.2) shallow crustal earthquakes: a comparison with predictions from eight recent ground-motion models

Strong-motion data from large (M ≥ 7.2) shallow crustal earthquakes invariably make up a small proportion of the records used to develop empirical ground motion prediction equations (GMPEs). Consequently GMPEs are more poorly constrained for large earthquakes than for small events. In this article peak ground accelerations (PGAs) observed in 38 earthquakes worldwide with M ≥ 7.2 are compared with those predicted by eight recent GMPEs. Well over half of the 38 earthquakes were not considered when deriving these GMPEs but the data were identified by a thorough literature review of strong-motion reports from the past 60 years. These data are provided in an electronic supplement for future investigations on ground motions from large earthquakes. The addition of these data provides better constraint of the between-event ground-motion variability in large earthquakes. It is found that the eight models generally provide good predictions for PGAs from these earthquakes, although there is evidence for slight under- or over-prediction of motions by some models (particularly for M > 7.6). The between-event variabilities predicted by most models match the observed variability, if data from two events (2001 Bhuj and 2005 Crescent City) that are likely atypical of earthquakes in active regions are excluded. For some GMPEs there is evidence that they are over-predicting PGAs in the near-source region of large earthquakes as well as over-predicting motions on hard rock. Overall, however, all the considered models, despite having been derived using limited data, provide reliable predictions of PGAs in the largest crustal earthquakes.

Strong ground motion observations of engineering interest from the 14 November 2016 Mw7.8 Kaikōura, New Zealand earthquake

This paper provides a brief discussion of observed strong ground motions from the 14 November 2016 Mw7.8 Kaikōura earthquake. Specific attention is given to examining observations in the near-source region where several ground motions exceeding 1.0g horizontal are recorded, as well as up to 2.7g in the vertical direction at one location. Ground motion response spectra in the near-source, North Canterbury, Marlborough and Wellington regions are also examined and compared with design levels. Observed spectral amplitudes are also compared with predictions from empirical and physics-based ground motion modelling.

Rupture process of the main shock of the 2016 Kumamoto earthquake with special reference to damaging ground motions: waveform inversion with empirical Green\u2019s functions

In this study, the rupture process of the main shock of the Kumamoto earthquake, particularly the generation of strong ground motions in the frequency range relevant to structural damage, was investigated based on the inversion of strong ground motions. Strong-motion records in the near-source region were mainly utilized because the authors were interested in the generation mechanism of damaging ground motions in the near-source region. Empirical Green’s functions (EGFs) were applied to avoid uncertainty in the subsurface structure model. Four cases of inversions with different combinations of small events were used to investigate the dependence of the inversion results on the selection of the small events. It was found that the dependence of the final slip distribution and peak slip velocity distribution on the selection of the EGF events is small. The results clearly indicate that a region of significantly large slip and slip velocity existed approximately 15 km northeast of the hypocenter. However, no “asperity” was observed between the hypocenter and Mashiki. Thus, it is not appropriate to conclude that the large-amplitude pulse-like ground motion in Mashiki was generated by the forward-directivity effect associated with the rupture of an asperity. As far as the source effect is concerned, the ground motion in Mashiki cannot be interpreted as the worst case scenario. On the other hand, the rupture of the “asperity” 15 km northeast of the hypocenter should have caused significantly large ground motions in regions close to the asperity. The significant damage of highway bridges in the region can potentially be attributed to the rupture of the asperity. The result of this study was compared with an inversion result obtained from numerical Green’s functions for a layered half-space. The two results share the main features in spite of the difference of the Green’s functions and stations used. Therefore, it can be concluded that these two source models capture the main features of the rupture process of the earthquake.Graphical abstractIn this study, the rupture process of the main shock of the Kumamoto earthquake, particularly the generation of strong ground motions in the frequency range relevant to structural damage, was investigated based on the inversion of strong ground motions. Strong-motion records in the near-source region were mainly utilized because the authors were interested in the generation mechanism of damaging ground motions in the near-source region. Empirical Green’s functions (EGFs) were applied to avoid uncertainty in the subsurface structure model. Four cases of inversions with different combinations of small events were used to investigate the dependence of the inversion results on the selection of the small events. It was found that the dependence of the final slip distribution and peak slip velocity distribution on the selection of the EGF events is small. The results clearly indicate that a region of significantly large slip and slip velocity existed approximately 15 km northeast of the hypocenter. However, no “asperity” was observed between the hypocenter and Mashiki. Thus, it is not appropriate to conclude that the large-amplitude pulse-like ground motion in Mashiki was generated by the forward-directivity effect associated with the rupture of an asperity. As far as the source effect is concerned, the ground motion in Mashiki cannot be interpreted as the worst case scenario. On the other hand, the rupture of the “asperity” 15 km northeast of the hypocenter should have caused significantly large ground motions in regions close to the asperity. The significant damage of highway bridges in the region can potentially be attributed to the rupture of the asperity. The result of this study was compared with an inversion result obtained from numerical Green’s functions for a layered half-space. The two results share the main features in spite of the difference of the Green’s functions and stations used. Therefore, it can be concluded that these two source models capture the main features of the rupture process of the earthquake.

Physics-based seismic input for engineering applications: a case study in the Aterno river valley, Central Italy

In this paper, we present 3D physics-based numerical simulations, in the near-source region at the regional scale, of the 2009, April 6, L’Aquila earthquake (central Italy), based on improved models of the Aterno river basin geology and source kinematics. The simulations were carried out by an open-source code, SPEED, based on a discontinuous Galerkin spectral element method. The numerical mesh of the Aterno basin was built on a detailed subsurface geological model and on the evaluation of the dynamic properties of the soils. The source model was selected among the kinematic solutions available in the literature as the one that fits best the near-source observations. Broadband ground motions were then generated through a hybrid method, combining 3D low frequency waveforms with high-frequency stochastic synthetics. To provide an example of application as seismic input to earthquake engineering analyses in the time domain, results of this approach were used for 2D site response analyses at Castelnuovo, a village severely damaged by the earthquake, and in the neighborhood of which no seismic record was available. SPEED simulation satisfactorily reproduces the recorded accelerograms in the frequency range 0.1–0.7 Hz. The site response analysis at the local scale shows that the amplification of the hill is more significant at its natural frequency, due to topographic and stratigraphic factors, than at the peak of the seismic input simulated by SPEED, that is at about 3 s along the fault-normal component. The presented application supports the conclusion that 3D physics-based numerical simulations do have the potential to become an alternative for determination of input ground motion for earthquake engineering analyses, especially for those scenarios for which real records are not available.

Stochastic Earthquake Rupture Modeling Using Nonparametric Co-Regionalization

Accurate predictions of the intensity and variability of ground motions are essential in simulation-based seismic hazard assessment. Advanced simulation-based ground motion prediction methods have been proposed to complement the empirical approach, which suffers from the lack of observed ground motion data, especially in the near-source region for large events. It is important to quantify the variability of the earthquake rupture process for future events and to produce a number of rupture scenario models to capture the variability in simulation-based ground motion predictions. In this study, we improved the previously developed stochastic earthquake rupture modeling method by applying the nonparametric co-regionalization, which was proposed in geostatistics, to the correlation models estimated from dynamically derived earthquake rupture models. The nonparametric approach adopted in this study is computationally efficient and, therefore, enables us to simulate numerous rupture scenarios, including large events (M>7.0). It also gives us an opportunity to check the shape of true input correlation models in stochastic modeling after being deformed for permissibility. We expect that this type of modeling will improve our ability to simulate a wide range of rupture scenario models and thereby predict ground motions and perform seismic hazard assessment more accurately.

Grammage of cosmic rays around Galactic supernova remnants

The residence time of cosmic rays (CRs) in the Galaxy is usually inferred from the measurement of the ratio of secondary-to-primary nuclei, such as the boron (B)/carbon (C) ratio, which provides an estimate of the amount of matter traversed by CRs during their propagation, the so called CR grammage. However, after being released by their parent sources, for instance supernova remnants (SNRs), CRs must cross the disc of the Galaxy, before entering the much lower density halo, in which they are believed to spend most of the time before eventually escaping the Galaxy. In the near-source region, the CR propagation is shown to be dominated by the non-linear self-generation of waves. Here we show that due to this effect, the time that CRs with energies up to $\sim$ 10 TeV spend within a distance $L_{c}\sim 100$ pc from the sources is much larger than naive estimates would suggest. The corresponding grammage is close to current estimates of the total grammage traversed throughout the whole Galaxy. Moreover, there is an irreducible grammage that CRs traverse while trapped downstream of the shock that accelerated them, though this contribution is rather uncertain. We conclude that at energies $\lesssim 1$ TeV, the observed grammage is heavily affected by the near-source non-linear trapping of CRs, and at energies $\gtrsim 1$ TeV it is affected by the source grammage. As a result, the measurement of the B/C ratio should be used very cautiously as an indicator of the propagation of CRs on large Galactic scales.

Near-source grid-based measurement of CO and PM2.5 concentration during a full-scale fire experiment in southern European shrubland

There is limited research on the exposure of wildland firefighters to smoke because of the operational obstacles when monitoring air pollutants in the field. In this work, a grid of portable sensors was used to measure PM2.5 and CO concentrations in the near-source region during the burn of two shrubland research blocks in Central Portugal. Strong spatial variability of smoke levels was observed in the analysis of the ratios between mean concentrations of neighbouring sensors, with values as high as 4.4 for PM2.5 and 7.4 for CO. These large gradients were registered at a distance of only 5 m suggesting that considerable differences on individual exposure can occur depending on the location of that individual in relation to the smoke plume trajectory. Also, peak events of 2–3 times the mean were observed in periods exceeding 6 min. In the two experiments, the average concentrations of both PM2.5 and CO were higher during smouldering, which represents a risk of acute exposure due to the closer proximity of firefighters to the emission source during mop-up, stressing the importance of wearing portable gas detectors for managing critical exposure. The collected data constitutes a step forward in the effort to understand the mechanisms controlling the exposure during firefighting operations, by providing a source of information on near-ground concentration fluctuations within a biomass-burning smoke plume at a fine spatial-temporal resolution.

Aerosol transport from Chiang Mai, Thailand to Mt. Lulin, Taiwan – Implication of aerosol aging during long-range transport

The transport of biomass burning (BB) aerosol from Indochina may cause a potential effect on climate change in Southeast Asia, East Asia, and the Western Pacific. Up to now, the understanding of BB aerosol composition modification during long-range transport (LRT) is still very limited due to the lack of observational data. In this study, atmospheric aerosols were collected at the Suthep/Doi Ang Khang (DAK) mountain sites in Chiang Mai, Thailand and the Lulin Atmospheric Background Station (Mt. Lulin) in central Taiwan from March to April 2010 and from February to April 2013, respectively. During the study period, an upwind and downwind relationship between the Suthep/DAK and Lulin sites (2400 km apart) was validated by backward trajectories. Comprehensive aerosol properties were resolved for PM2.5 water-soluble inorganic ions, carbonaceous content, water-soluble/insoluble organic carbon (WSOC/WIOC), dicarboxylic acids and their salts (DCAS), and anhydrosugars. A Modification Factor (MF) is proposed by employing non-sea-salt potassium ion (nss-K+) or fractionalized elemental carbon evolved at 580 °C after pyrolized OC correction (EC1-OP) as a BB aerosol tracer to evaluate the mass fraction changes of aerosol components from source to receptor regions during LRT. The MF values of nss-SO42−, NH4+, NO3−, OC1 (fractionalized organic carbon evolved from room temperature to 140 °C), OP (pyrolized OC fraction), DCAS, and WSOC were above unity, which indicated that these aerosol components were enhanced during LRT as compared with those in the near-source region. In contrast, the MF values of anhydrosugars ranged from 0.1 to 0.3, indicating anhydrosugars have degraded during LRT.

Papanoa, Mexico earthquake of 18 April 2014 (Mw7.3)

Papanoa earthquake broke the plate interface NW of the Guerrero seismic gap. In this region, previous large earthquakes occurred in 1943 (MS 7.4), 1979 (Mw7.4) and 1985 (Mw7.5). The earthquake was recorded in the near-source region by several accelerographs. Severe damage was reported in Papanoa (where PGA of ~ 0.9 g was recorded on one of the horizontal components at a soft site) and other nearby coastal towns. It was also felt strongly in Mexico City where the ground motions were comparable to those recorded during the 1979 and 1985 events. A careful analysis of the near-source data, including P-wave polarization, yields an epicenter at 17.375 ºN, 101.055 ºW, close to the coast, near the town of Papanoa. Effective duration of ground motion at near-source coastal stations to the NW of the epicenter is 10-15 s, while it is 20-35 s to the SE, demonstrating rupture directivity towards Zihuatanejo. Three (in some cases only two) bursts of high-frequency radiation are visible in the accelerograms. Near-field records show that the slip was small during the initial 2-3 s of rupture which, subsequently, cascaded in two or three larger subevents. Slip inversion using teleseismic waves, along with GPS data from a couple of near-source sites, reveals that the rupture mainly consisted of two subevents. The first one was centered close to the hypocenter and had a radius of ~ 15 km. The second subevent, roughly of the same dimension as the first, was centered ~ 25 km SSE of Zihuatanejo. Previous analysis of three slow slip events (SSEs) in the region (2001-2002; 2006; 2009-2010) had revealed that this region had a high inter-SSE coupling ratio (&gt; 0.5) with a slip deficit about four times greater than in the adjacent NW Guerrero seismic gap (Radiguet et al., 2012). It seems that the large slip patch corresponding to the first subevent of the 2014 earthquake experienced a cumulative slip of ~ 20 cm during the SSEs, suggesting that seismic and SSE slip may share the same area of the interface. Alternatively, the SSE slip may have occurred over an area surrounding the large slip patch, a physically more plausible model. Epicenters of aftershocks (M ≥ 3.5), which occurred in the next 36 hours, define a rectangular area of ~ 40 km • 70 km, oriented ~ N75ºE; about half of this area lies onshore. This area encloses the inverted slip region. More than half of the aftershock area overlaps with that of the 1979 earthquake and a small fraction with that of the 21 September 1985 earthquake. As we only know the slip distribution of the 2014 earthquake, it is not known if the two large-slip patches had also slipped similarly during the previous earthquakes. The earthquake was followed by two moderately large events that occurred on 8 May (Mw6.5) and 10 May (Mw6.1). The epicenters of these events fall near Tecpan, within the NW Guerrero seismic gap (which extends from 100 ºW to 101 ºW), outside the aftershock area of the Papanoa earthquake. No large earthquake has occurred in this part of the gap, between Papanoa and Acapulco, since the events of 1899 (MS7.5) and 1911 (MS7.6). However, seismicity in the region (at Mw ≥ 5 level) appears normal. A few moderate earthquakes of unusually large duration and deficient high-frequency radiation have been identified near the trench. In contrast to the Papanoa - Zihuatanejo region, in this segment the inter-SSE coupling ratio from ~ 10 km inland towards sea is very low (&lt; 0.2) and the slip deficit is about one-fourth that of the Papanoa- Zihuatanejo region (Radiguet et al., 2012). As a consequence, the expected recurrence period of large/great earthquakes may be relatively long, in agreement with the seismicity of the Papanoa-Acapulco region.