Seismogram Modeling Research Articles

Multiscale Full-Waveform Inversion with Land Seismic Field Data: A Case Study from the Jizhong Depression, Middle Eastern China

The Jizhong depression contains several geothermal reservoirs that are characterized by localized low-velocity anomalies. In this article, full-waveform inversion (FWI) is used to characterize these anomalies and determine their extent. This is a challenging problem because the reservoirs are quite small and the available data have usable frequencies only down to 5 Hz. An accurate-enough starting model is carefully built by using an iterative travel time tomography method combined with a cycle-skipping assessment method to begin the inversion at 5 Hz. A multiscale Laplace–Fourier-domain FWI with a layer-stripping approach is implemented on the starting model by gradually increasing the maximum offset. The result of overlapping the recovered velocity model on the migrated seismic profile shows a good correlation between the two results. The recovered model is assessed by ray tracing, synthetic seismogram modeling, checkerboard testing and comparisons with nearby borehole data. These tests indicate that low-velocity anomalies down to a size of 0.3 km × 0.3 km at a maximum depth of 2 km can be recovered. Combined with the well log data, the resulting velocity model allows us to delineate two potential geothermal resources, one of which was previously unknown.

Ultralow-frequency amplitude variation with angle inversion of plane-wave primary reflection seismograms

An amplitude variation with angle (AVA) inversion method is presented for estimating density and velocities of a stratified elastic medium from reflection seismograms in the intercept time-horizontal slowness domain. The elastic medium parameters are assumed to vary continuously with depth. The seismograms are Green’s function precritical incidence primary P-wave reflections of time length [Formula: see text], assumed to obey differential equations of a model for elastic primary P-wave backscattering, similar to seismograms representing the first term in the well-known Bremmer series/Wentzel–Kramers–Brillouin–Jeffreys iterative solution model. A relation is found between the plane-wave Green’s function seismograms at each horizontal slowness and the medium properties in time. The Green’s function seismograms after normal-moveout correction are directly inverted for the medium parameters as a function of zero-offset traveltime. It is documented theoretically and verified numerically that the signal at the fundamental frequency [Formula: see text] must be present in the seismograms for the AVA method to provide the parameter trends of the elastic medium, implying that ultralow frequencies <1 Hz for [Formula: see text] s must be generated and recorded. Noise in the seismograms at ultralow frequencies is not considered because the theoretical AVA model does not handle microseisms that would be measured in real data. The main mathematical findings are illustrated by using simple model seismograms.

Insights from synthetic seismogram modelling study of oceanic lower crust and Moho Transition Zone

The Moho discontinuity is one of the fundamental boundaries on Earth, separating the crust from the upper mantle. Arrival times of seismic reflection and refraction data are used to estimate the depth of the Moho, but the nature of the Moho remains illusive. We present a synthetic seismogram modelling study for a suite of possible velocity models of the oceanic lower crust and Moho transition zone (MTZ). For modelling, we have used a 45-km long multichannel streamer (MCS) geometry, to get insight about waveforms and amplitudes of seismic phases like the crustal refraction (Pg), Moho reflection (PmP) and mantle refraction (Pn), and the interactions between these phases. We find that the nature of PmP reflection not only depends on the velocity structure of the MTZ but also on the velocity structure of the lower crust and upper mantle. The triplication resulting from these three seismic arrivals and its lateral extent mainly depend on the velocity structure in the lower crust. Apart from the velocity in the crust, the critical distance for the PmP arrival depends on the velocity gradient in the MTZ. The amplitude versus offset analysis of the wide-angle PmP arrivals indicates that there are two broad high amplitude peaks for the MTZ thickness less than or equal to the dominant seismic wavelength and only one large narrow peak for a thicker MTZ. Consequently, strong PmP arrivals for a thick MTZ lie in a narrow offset range around the critical offset whereas they lie over a large offset range for a sharp Moho. We also have modelled the synthetic seismograms for velocity structures from the Oman and the Bay of Islands ophiolites. Our modelling results indicate that the quantitative analysis of amplitudes and waveforms of ultra-long offset MCS data could provide detailed information about the lower crust and MTZ.

FDwave3D: a MATLAB solver for the 3D anisotropic wave equation using the finite-difference method

Seismic modeling plays an important role in geophysics and seismology for estimating the response of seismic sources in a given medium. In this work, we present a MATLAB-based package, FDwave3D, for synthetic wavefield and seismogram modeling in 3D anisotropic media. The seismic simulation is carried out using the finite-difference method over the staggered grid, and it is applicable to both active and passive surveys. The code package allows the incorporation of arbitrary source mechanisms and offers spatial derivative operators of accuracy up to tenth-order along with different types of boundary conditions. First, the methodological aspects of finite-difference method are briefly introduced. Then, the code has been tested and verified against the analytical solutions obtained for the homogeneous model. Further, the numerical examples of layered and overthrust models are presented to demonstrate its reliability.

Physical properties and core-log seismic integration from drilling at the Danube deep-sea fan, Black Sea

Abstract Drilling, coring, and geophysical logging were performed with the MARUM-MeBo200 seafloor drilling rig to investigate gas hydrate occurrences of the Danube deep sea fan, off Romania, Black Sea. Three sites within a channel-levee complex were investigated. Geophysical log data of P-wave velocity, electrical resistivity, and spectral gamma ray are combined with core-derived physical properties of porosity, magnetic susceptibility, and bulk density. Core- and log physical property data are used to define a time-depth conversion by synthetic seismogram modeling, which is then used to interpret the seismic data. Individual polarity reversed reflectors within the stratigraphic column drilled are linked to reduction in P-wave velocity and bulk density. Those reflectors (and associated reflection packages) are accompanied by distinct and systematic changes in sediment porosity, magnetic susceptibility, and electrical resistivity. Overall, the sediments at drill site GeoB22605 (MeBo-17) represent the younger (upper) levee sequence of the channel, that has been eroded at drill site GeoB22603 (MeBo-16). Splicing seismic data across the channel from the East (MeBo-16) to the West (MeBo-17) demonstrates the continuation of reflectors underneath the channel. The upper ~50 m below seafloor (mbsf) at site MeBo-16 do not stratigraphically belong to the same sequence of the (deeper) levee-deposits. Above the marked erosional unconformity, sediments at Site MeBo-16 are likely derived by a mixture of repeated slump-events (identified as seismically transparent units) interbedded with hemi-pelagic sedimentation. Similarly, sediments within the upper ~20 mbsf at Site MeBo-17 are not stratigraphically the same levee-deposits, but are derived by a mixture of slump-events (also seen in the marked seafloor amphitheatre architecture of a large failure complex extending further upslope) and hemi-pelagic sedimentation. All observations combined show that the seismically observed stratigraphic pattern represents a reflectivity sequence mostly driven by variations in density (porosity) and correspondingly by changes in P-wave velocity and electrical resistivity. Observations from the geophysical log- and core, as well as geochemical data, show no evidence for the presence of any significant gas hydrates within the drilled/cored sequences.

An approach of refraction seismology for processing and modeling of local earthquake seismogram sections of virtual sources at multiple depths in seismogenic regions—application to Koyna-Warna region, India, for upper crustal P and S velocity structure

We present an approach based on controlled source seismology (CSS) methods, especially developed for processing and modeling of the local earthquake seismograms. Record sections of the local earthquake seismograms generated for multiple source depths illuminate the upper crustal velocity structure in the region. Extensive travel times and synthetic seismograms modeling of the observed record sections reveal the P and S velocity structure in the region. The strength of this approach essentially lies with the possibility of validating the upper crustal velocity models inferred in various subregions of the seismogenic region. A redundant and significantly large number of virtual source local earthquake seismogram sections, gathered for multiple source depths and varying source mechanisms in each of the subregions, validate the same set of P and S velocity models in that region. Further, those models are found to generate the synthetic seismograms consistent with the observed sections. The proposed approach effectively utilizes a reliable dataset from a great volume of well-located local earthquake recordings of a state-of-the-art digital seismograph network. Such a dataset of local earthquake seismograms in the Koyna-Warna active earthquake zone is used here to demonstrate this approach and obtained subregion-specific models of upper crustal P and S velocity structure in the epicentral region. The results indicate that the technique presented here is efficient for processing and modeling the local earthquake seismograms and deriving upper crustal velocity models in the seismogenic regions.

On the role of density and attenuation in three-dimensional multiparameter viscoacoustic VTI frequency-domain FWI: an OBC case study from the North Sea

3-D frequency-domain full waveform inversion (FWI) is applied on North Sea wide-azimuth ocean-bottom cable data at low frequencies (≤10 Hz) to jointly update vertical wave speed, density and quality factor Q in the viscoacoustic VTI approximation. We assess whether density and Q should be viewed as proxy to absorb artefacts resulting from approximate wave physics or are valuable for interpretation in the presence of soft sediments and gas cloud. FWI is performed in the frequency domain to account for attenuation easily. Multiparameter frequency-domain FWI is efficiently performed with a few discrete frequencies following a multiscale frequency continuation. However, grouping a few frequencies during each multiscale step is necessary to mitigate acquisition footprint and match dispersive shallow guided waves. Q and density absorb a significant part of the acquisition footprint hence cleaning the velocity model from this pollution. Low Q perturbations correlate with low-velocity zones associated with soft sediments and gas cloud. However, the amplitudes of the Q perturbations show significant variations when the inversion tuning is modified. This dispersion in the Q reconstructions is however not passed on the velocity parameter suggesting that cross-talks between first-order kinematic and second-order dynamic parameters are limited. The density model shows a good match with a well log at shallow depths. Moreover, the impedance built a posteriori from the FWI velocity and density models shows a well-focused image with however local differences with the velocity model near the sea bed where density might have absorbed elastic effects. The FWI models are finally assessed against time-domain synthetic seismogram modelling performed with the same frequency-domain modelling engine used for FWI.

Seismic inversion for geologic fractures and fractured media

Amplitude variation with offset (AVO) inversion attempts to use the available surface seismic data to estimate the density, P-wave velocity, and S-wave velocity of the earth model. Under linear slip interface theory, synthetic seismograms for models with fractures prove that fractures are also reflection generators. Consequently, observed reflections are not necessarily due to lithologic variations only, but they could be due in part to the effect of fractures. To obtain approximate equations for AVO inversion for fractured media, denoted by AVO with fracture (AVOF), we derived new equations for PP-wave reflection and transmission coefficients that are based on nonwelded contact boundary conditions. In particular, along with the fracture compliances, azimuth has also been taken into account in the equations because the fractures can have any orientation. The new approximate AVOF equations for a horizontally fractured medium with impedance contrast are developed by simplifying the equations for the new PP-wave reflection and transmission coefficients. In the new approximate AVOF equations, the reflection coefficients are divided into a welded contact part (a conventional impedance contrast part) and a nonwelded contact part (a fracture part). This makes the equations flexible enough to separately invert for the rock properties of the fracture and the background medium in the case of a fractured medium with impedance contrast. The new approximate AVOF equations state that fractures could cause the seismic reflectivity to be frequency dependent, and that the fractures not only influence the wave amplitude but also change the wave phase. The linear least-squares and nonlinear conjugate gradient inversion algorithms are applied to estimate the elastic reflectivity using the new approximate AVOF equations. The inverted results for seismic data for a horizontally fractured medium with impedance contrast are evaluated to find a more accurate delineation of the subsurface rock properties.

Toward a robust workflow for deep crustal imaging by FWI of OBS data: The eastern Nankai Trough revisited

AbstractCrustal‐scale imaging by the full‐waveform inversion (FWI) of long‐offset seismic data is inherently difficult because the large number of wavelengths propagating through the crust makes the inversion prone to cycle skipping. Therefore, efficient crustal‐scale FWI requires an accurate starting model and a stable workflow minimizing the nonlinearity of the inversion. Here we attempt to reprocess a challenging 2‐D ocean‐bottom seismometer (OBS) data set from the eastern Nankai Trough. The starting model is built by first‐arrival traveltime tomography (FAT), which is FWI assisted for tracking cycle skipping. We iteratively refine the picked traveltimes and then reiterate the FAT until the traveltime residuals remain below the cycle‐skipping limit. Subsequently, we apply Laplace‐Fourier FWI, in which progressive relaxation of time damping is nested within frequency continuation to hierarchically inject more data into the inversion. These two multiscale levels are complemented by a layer‐stripping approach implemented through offset continuation. The reliability of the FWI velocity model is assessed by means of source wavelet estimation, synthetic seismogram modeling, ray tracing modeling, dynamic warping, and checkerboard tests. Although the viscoacoustic approximation is used for wave modeling, the synthetic seismograms reproduce most of the complexity of the data with a high traveltime accuracy. The revised FWI scheme produces a high‐resolution velocity model of the entire crust that can be jointly interpreted with migrated images derived from multichannel seismic data. This study opens a new perspective on the design of OBS crustal‐scale experiments amenable to FWI; however, a further assessment of the optimal OBS spacing is required for reliable FWI.

Red Sea isolation history suggested by Plio-Pleistocene seismic reflection sequences

High evaporation rates in the desert climate of the Red Sea ensure that, during glacial sea level lowstands when water exchange with the Indian Ocean was more restricted, water salinity and δ18O became unusually extreme. Modeling of the effect on Red Sea sedimentary δ18O has been used previously to reconstruct relative sea level to 500 ka and now poses the question of whether that sea-level model could be extended if continuous core material of older sediment became available. We attempt to address this question here by examining seismic reflection data. The upper Pleistocene hemipelagic sediments in the Red Sea contain intervals of inorganic aragonite precipitated during supersaturated conditions of sea-level lowstands. Seismic impedance changes associated with boundaries to those aragonite-rich layers appear to explain seismic reflection sequences. A segment of Chirp sediment profiler data from the central Red Sea reveals prominent reflections at ∼1, ∼5, ∼23, ∼26 and ∼36 ms two-way travel time (TWT) from the seabed. Based on depths to the glacial marine isotope stages (MIS) in cores, we relate the upper three reflections to the tops of aragonite-rich layers and hence the sea level rises immediately following MIS 2, 6 and 12. The reflection at 26 ms is related to an unusually rapid fall into MIS 12 predicted by one sea level reconstruction, which may have created an abrupt lower boundary to the MIS 12 aragonite-rich layer. With the aid of seismogram modeling, we tentatively associate the ∼36 ms reflection with the top of an aragonite-rich layer formed during MIS 16. Furthermore, some segments of lower frequency (airgun and sparker) seismic data from the central and southern Red Sea show a lower (earlier) Plio-Pleistocene (PP) interval that is less reflective than the upper (late) PP interval. This implies less variability in sediment impedance and that extreme variability in water salinity did not develop; water exchange with the Indian Ocean likely continued throughout this interval. These results suggest that viable relative sea level reconstructions may be recovered from Red Sea sediment δ18O data to at least MIS 16 and perhaps even as far back as the early Pliocene.

Seismic Evidence of Ancient Westward Residual Slab Subduction Beneath Southern Taiwan

The northeastern convergence of the Philippine Sea plate toward the Eurasian plate causes the major western Philippine Sea plate boundary to subduct toward the northwest or west directions. However, this phenomenon is not clearly observed along the plate boundary between Luzon and Taiwan. Careful examination of deep seismicity in the southern Taiwan area from the earthquake catalog reported by the Central Weather Bureau shows two seismic zones dipping toward the opposing directions. The first dips toward the east from the surface down to 150 km in depth, while the second dips westward at depths between 150 and 200 km. These two seismic zones are confirmed further by seismogram observation and modeling results generated by two deep faults in the southern Taiwan area. The eastward seismic zone clearly results from the Eurasia plate subduction along the Manila trench, while a small section of the westward seismic zone might likely be a residual slab from the ancient subducted Philippine Sea plate. Based on the subduction speed obtained from GPS observations and the subducted Eurasian plate geometry, we can further estimate the eastward Eurasian plate subduction started at least 3.35 million years ago. This result is roughly consistent with the volcanic ages (3 - 4 Ma) observed in the arc between Luzon and Taiwan.

Broadband Ground-Motion Simulation Using Energy-Constrained Rise-Time Scaling

Abstract The simulation of realistic ground motions associated with large earthquakes is of utmost importance for engineering concerns, for example, in testing the seismic performance of buildings. It is also needed to estimate the level of ground shaking for future earthquakes. In this paper, we focus on two aspects of ground‐motion modeling. First, we use deterministic wave propagation for the entire frequency range but account for source variability by implementing self‐similar slip distributions and rough fault interfaces. Second, we scale the rise time of the source time function so that the modeled waveforms represent the correct radiated seismic energy. The method is validated for the 2008 Wenchuan, China, earthquake and the 2003 Tokachi‐Oki, Japan, earthquake. We demonstrate the robustness of our approach with regard to changes of the assumed rupture velocity. We find the fine source discretizations combined with the small scale source variability ensure that the high frequencies (1–8 Hz) are satisfactorily introduced, justifying the deterministic wave propagation approach even at high frequencies. The adjustment of the rise time via the radiated seismic energy permits a simulation without making assumptions on the stress drop, as is usually done by other modeling approaches. By varying different parameters, such as the energy magnitude, the simulation approach could be especially useful for estimating the range of possible ground motions issuing from a distinct fault in a future earthquake. The rise‐time scaling may also be used for seismogram modeling in the context of early‐response systems as the energy magnitude, which is the parameter needed for the scaling, is available shortly after the earthquake. Online Material: Tables of kinematic rupture models for 2008 Wenchuan and 2003 Tokachi‐Oki, and Fourier spectra of simulations.

Seismic visibility of a deep subduction channel – insights from numerical simulation of high-frequency seismic waves emitted from intermediate depth earthquakes

Abstract. Return flow in a deep subduction channel (DSC) has been proposed to explain rapid exhumation of high pressure–low temperature metamorphic rocks, entirely based on the fossil rock record. Supported by thermo-mechanical models, the DSC is envisioned as a thin layer on top of the subducted plate reaching down to minimum depths of about 150 km. We perform numerical simulations of high-frequency seismic wave propagation (1–5 Hz) to explore potential seismological evidence for the in situ existence of a DSC. Motivated by field observations, for modeling purposes we assume a simple block-in-matrix (BIM) structure with eclogitic blocks floating in a serpentinite matrix. Homogenization calculations for BIM structures demonstrate that effective seismic velocities in such composites are lower than in the surrounding oceanic crust and mantle, with nearly constant values along the entire length of the DSC. Synthetic seismograms for receivers at the surface computed for intermediate depth earthquakes in the subducted oceanic crust for models with and without DSC turn out to be markedly influenced by its presence or absence. While for both models P and S waveforms are dominated by delayed high-amplitude guided waves, models with DSC exhibit a very different pattern of seismic arrivals compared to models without DSC. The main reason for the difference is the greater length and width of the low-velocity channel when a DSC is present. Seismic velocity heterogeneity within the DSC or oceanic crust is of minor importance. The characteristic patterns allow for definition of typical signatures by which models with and without DSC may be discriminated. The signatures stably recur in slightly modified form for earthquakes at different depths inside subducted oceanic crust. Available seismological data from intermediate depth earthquakes recorded in the forearc of the Hellenic subduction zone exhibit similar multi-arrival waveforms as observed in the synthetic seismograms for models with DSC. According to our results, observation of intermediate depth earthquakes along a profile across the forearc may allow to test the hypothesis of a DSC and to identify situations where such processes could be active today.

Global synthetic seismograms using a 2-D finite-difference method

Two-dimensional (2-D) finite-difference (FD) synthetics, which fill the gap between fast 1-D analytic synthetics and time-consuming full 3-D synthetics in our ability to model seismograms, have been used in many studies. We address several issues involving 2-D FD methods in generating global synthetic seismograms. These include: (1) interfacing point source excitation for earthquakes with 2-D FD methods; (2) out-of-plane spreading corrections and (3) reducing the spherical Earth to the flattened models. The first issue is tackled using two methods, a ‘transparent source box’ approach and a moment tensor excitation approach, where each has its own advantages. Moreover, our ‘source box’ excitation does not have the late-time drift problem that occurred in previous studies. The out-of-plane geometric spreading correction is accounted for by estimating the ray parameter and applying a post-simulation filter to 2-D synthetics. Finally, parameters of the Earth-flattening transformation are discussed and validated. The effectiveness of this method is demonstrated by comparing our synthetics with frequency–wavenumber summation, normal-mode and 3-D spectral-element synthetics.

Better Perceptive and Enhanced Visualization of Seismic Profiles for the Exploration of Hydrocarbon Using a Seismic and Synthetic Seismogram Modeling of Khipro Block, Southern Indus Basin, Sindh Province, Pakistan

Seismic and well log interpretation is done using synthetic modeling in the lower Indus basin, Khipro Block for search of suitable traps and reservoir conditions favorable for hydrocarbon accumulation in Lower Goru and Basal Sand. A synthetic seismogram was used to tie well tops and seismic profiles to mark horizons correctly. Well zonation revealed that average porosity ranges from 16–19% and volume of shale ranges from 15–50%. Two zones in Naimat Basal 01 can be perspective units. On the basis of seismic interpretation, test well location is proposed.

Velocity modeling of a complex deep crustal structure across the Mesoproterozoic south Delhi Fold Belt, NW India, from joint interpretation of coincident seismic wide-angle and near-offset reflection data: An approach using unusual reflections in wide-angle records

[1] Seismic wide-angle record sections from favorably placed source and limited-aperture recording spreads, particularly across collision boundaries, reveal bright unusual high-velocity contrast reflections of limited lateral coherence. The arrival times of the unusual reflections for recording updip of the reflecting plane align as high apparent velocity phases at wide-angle offsets. Coincident near-offset reflection images from similar structural features provide additional control for modeling the unusual phases on the wide-angle record sections. We propose an approach for joint interpretation of these coincident seismic data sets and modeling the unusual phases on the processed wide-angle records to delineate both the velocity stratification and the geometry of the deep crustal structures consistent with the near-offset reflection images. Processed and migrated near-offset reflection images reveal several steeply dipping isolated reflections on the western margin of the south Delhi Fold Belt (DFB), NW India, interpreted as the south Delhi thrust fault. Coincident limited-aperture, wide-angle records reveal bright unusual reflections, which are also found to be associated with the same thrust fault. Observations of similar dipping reflection patterns in various other regions lend support to consider them as genuine in-plane reflections resulting from a structural fabric imprinted on horizontally oriented geological structures. We use the reflectivity structural model from the near-offset data set that provides necessary constraints for modeling and simulating the travel times and amplitudes of the unusual reflections recognized in the wide-angle records. The unusual reflections are effectively used as part of the wide-angle data set for Gaussian beam synthetic seismogram modeling, thus delineating for the first time a complex 2-D model of the seismic velocity structure of the deep crust and uppermost mantle across the Marwar Basin (MB) and the DFB. The dipping events revealed in the wide-angle data set are successfully modeled and interpreted as reflections from the thrust fault, consistent with the near-offset reflection image. The 2-D velocity model, parameterized as a stack of isolated dipping reflectors embedded in deep crustal layers, is successively refined by including the structural features recognizable both in the near-offset reflection image and in the wide-angle records. The unusual reflections are modeled as a set of discrete reflectors representing local velocity variations imprinted on the background of a deep crustal velocity structure. The lamellar structure revealed by short, isolated dipping and the subhorizontal middle to lower crustal reflections suggests heterogeneities at scale lengths on the order of at least the Fresnel zone diameter as resolved here. The local velocity variations in the deep crust can be considered analogous, on a different scale, to the models in which velocity heterogeneities on scale lengths of the seismic wavelength constitute a medium of random distribution of scatterers. The crustal-scale south Delhi thrust fault on the western margin of the DFB, delineated as the stack of reflectors dipping 25°–30°SE, probably developed during the Mesoproterozoic collisional episode related to the Delhi orogeny, contemporaneous with the formation of Rodinia. It is concluded that complex structural features developed during collisional episodes can survive through geological periods, longer than generally expected, depending on the accretionary characteristics at the time of orogenic evolution. The 2-D velocity model further reveals significant variations of crustal seismic structure, with a relatively sharp and shallow Moho (at 39–40 km) in the MB and a deeper Moho (at 45–47 km) underlying a 12 km thick subhorizontal lamella of high-velocity (6.9–7.5 km/s) layers in the DFB regions.

Reply to "Comment on `The 28 December 1908 Messina Straits Earthquake (Mw 7.1): A Great Earthquake throughout a Century of Seismology,' by N. A. Pino, A. Piatanesi, G. Valensise, and E. Boschi" by A. Amoruso, L. Crescentini, and R. Scarpa

Research Article| March 01, 2010 Reply to “Comment on `The 28 December 1908 Messina Straits Earthquake (Mw 7.1): A Great Earthquake throughout a Century of Seismology,' by N. A. Pino, A. Piatanesi, G. Valensise, and E. Boschi” by A. Amoruso, L. Crescentini, and R. Scarpa Nicola Alessandro Pino; Nicola Alessandro Pino Istituto Nazionale di Geofisica e Vulcanologia Sezione di Napoli, Osservatorio Vesuviano Via Diocleziano 328 80124 Naples, Italy alessandro.pino@ov.ingv.it (N. A. P.) Search for other works by this author on: GSW Google Scholar Alessio Piatanesi; Alessio Piatanesi Istituto Nazionale di Geofisica e Vulcanologia Sezione di Napoli, Osservatorio Vesuviano Via Diocleziano 328 80124 Naples, Italy alessandro.pino@ov.ingv.it (N. A. P.) Search for other works by this author on: GSW Google Scholar Gianluca Valensise; Gianluca Valensise Istituto Nazionale di Geofisica e Vulcanologia Sezione di Napoli, Osservatorio Vesuviano Via Diocleziano 328 80124 Naples, Italy alessandro.pino@ov.ingv.it (N. A. P.) Search for other works by this author on: GSW Google Scholar Enzo Boschi Enzo Boschi Istituto Nazionale di Geofisica e Vulcanologia Sezione di Napoli, Osservatorio Vesuviano Via Diocleziano 328 80124 Naples, Italy alessandro.pino@ov.ingv.it (N. A. P.) Search for other works by this author on: GSW Google Scholar Author and Article Information Nicola Alessandro Pino Istituto Nazionale di Geofisica e Vulcanologia Sezione di Napoli, Osservatorio Vesuviano Via Diocleziano 328 80124 Naples, Italy alessandro.pino@ov.ingv.it (N. A. P.) Alessio Piatanesi Istituto Nazionale di Geofisica e Vulcanologia Sezione di Napoli, Osservatorio Vesuviano Via Diocleziano 328 80124 Naples, Italy alessandro.pino@ov.ingv.it (N. A. P.) Gianluca Valensise Istituto Nazionale di Geofisica e Vulcanologia Sezione di Napoli, Osservatorio Vesuviano Via Diocleziano 328 80124 Naples, Italy alessandro.pino@ov.ingv.it (N. A. P.) Enzo Boschi Istituto Nazionale di Geofisica e Vulcanologia Sezione di Napoli, Osservatorio Vesuviano Via Diocleziano 328 80124 Naples, Italy alessandro.pino@ov.ingv.it (N. A. P.) Publisher: Seismological Society of America First Online: 09 Mar 2017 Online ISSN: 1938-2057 Print ISSN: 0895-0695 © 2010 by the Seismological Society of America Seismological Research Letters (2010) 81 (2): 229–231. https://doi.org/10.1785/gssrl.81.2.229 Article history First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Nicola Alessandro Pino, Alessio Piatanesi, Gianluca Valensise, Enzo Boschi; Reply to “Comment on `The 28 December 1908 Messina Straits Earthquake (Mw 7.1): A Great Earthquake throughout a Century of Seismology,' by N. A. Pino, A. Piatanesi, G. Valensise, and E. Boschi” by A. Amoruso, L. Crescentini, and R. Scarpa. Seismological Research Letters 2010;; 81 (2): 229–231. doi: https://doi.org/10.1785/gssrl.81.2.229 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietySeismological Research Letters Search Advanced Search This is a rather unusual comment that focuses on how a specific figure was constructed rather than on actual scientific results. The figure in question (Figure 9 from Pino et al. 2009) does not even show new data or results, but is simply a summary of slip models that have been proposed in the literature for the 1908 earthquake. All models describe slip distributions from coseismic elevation changes except for one, derived by Pino et al. (2000) based on waveform modeling of historical seismograms. To construct Figure 9 we simply plotted the slip maxima obtained by different... You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Faulting Parameters of Earthquakes (4.1 <= ML <= 5.3) in the Peninsular Ranges of Baja California, Mexico

Seismic moment ( M ) is a parameter related to the physical process that takes place at the source (Aki 1966; Aki and Richards 1980). Sometimes it is possible to calculate M from the constant spectral amplitude level at low frequencies, but in other cases this is not possible. For instance, for M > 4.0 earthquakes (recorded at short distances), it is difficult to determine the flat portion of the spectrum due to instrumental limitations. For these cases, waveform modeling is an alternative way to evaluate M . In addition to determining this source parameter, it is also possible to obtain the faulting geometry and the depth of the hypocenter through waveform modeling. In the Peninsular Ranges of Baja California (PRBC), few studies have been conducted to determine earthquake faulting parameters. Some examples are the studies of Nava and Brune (1983) (1975 ML 5.1 earthquake) and Gonzalez (1987) (1985 ML 5.0 earthquake). However, studies of the seismic source have not been attempted for earthquakes of lower magnitude ( M < 5). We computed the faulting parameters of five small-to-moderate earthquakes that occurred between 1991 and 1996 in the PRBC, via waveform modeling of broadband seismograms recorded at regional distances (180 to 245 km). Our modeling was important in constraining the fault plane orientation obtained from first-motion polarities recorded for those earthquakes. In this modeling, we considered epicenter-to-station paths of the Peninsular Ranges of southern California and Baja California tectonic regions. Historically, moderate size earthquakes (5 ≤ M ≤ 7) have occurred in the PRBC, mainly along the San Miguel fault. Examples of these earthquakes are the 1954 earthquakes ( M 6.0 and 6.4; Leeds 1979) and the 1956 earthquakes ( ML 6.8, 6.4 and 6.3; Shor and Roberts 1958). Castro (1983) used synthetic seismograms to calculate the seismic …

CRUSTAL VELOCITY STRUCTURE OF THE RUKWA RIFT IN THE WESTERN BRANCH OF THE EAST AFRICAN RIFT SYSTEM

Research Article| December 01, 2009 CRUSTAL VELOCITY STRUCTURE OF THE RUKWA RIFT IN THE WESTERN BRANCH OF THE EAST AFRICAN RIFT SYSTEM S. KIM; S. KIM School of Earth and Environmental Sciences, Seoul National University, Seoul, South Korea, e-mail: srk@snu.ac.kr Search for other works by this author on: GSW Google Scholar A.A. NYBLADE; A.A. NYBLADE Department of Geosciences, Pennsylvania State University, University Park, Pennsylvania, United States of America, e-mail: andy@geosc.psu.edu Search for other works by this author on: GSW Google Scholar C-E. BAAG C-E. BAAG School of Earth and Environmental Sciences, Seoul National University, Seoul, South Korea, e-mail: baagce@snu.ac.kr Search for other works by this author on: GSW Google Scholar South African Journal of Geology (2009) 112 (3-4): 251–260. https://doi.org/10.2113/gssajg.112.3-4.251 Article history first online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation S. KIM, A.A. NYBLADE, C-E. BAAG; CRUSTAL VELOCITY STRUCTURE OF THE RUKWA RIFT IN THE WESTERN BRANCH OF THE EAST AFRICAN RIFT SYSTEM. South African Journal of Geology 2009;; 112 (3-4): 251–260. doi: https://doi.org/10.2113/gssajg.112.3-4.251 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietySouth African Journal of Geology Search Advanced Search Abstract We investigate the thickness and seismic velocity structure of the Rukwa Rift crust by modeling seismograms from the 1994 Mw 5.9 Rukwa earthquake and teleseismic receiver functions recorded on a broadband seismic station at the southeastern end of the rift. Two methods have been used to model receiver functions, H-κ stacking and waveform inversion, yielding Moho depth estimates of 34 ± 2 km (H-κ stacking) and 38 ± 2 km (waveform inversion), and a crustal Poisson’s ratio of 0.27 ± 0.01 (H-κ stacking). A 1D average velocity model for the rifted crust has been obtained by trial-and-error modeling of the Rukwa earthquake seismograms. The best fitting velocity model obtained has a 4.5 km thick near-surface low-velocity section over a 33 km thick middle-to-lower crustal section. The velocities and thickness of the near-surface layers are consistent with the known thickness and composition of the sedimentary basin fill. The middle-to-lower crustal section is characterised by a linear velocity gradient with shear wave velocities of 3.9 km/s or higher at depths > 20 km. Crustal Poisson’s ratio in the model is 0.27. The Moho depth in the model (37.5 km) is similar to the Moho depth obtained from analysing receiver functions, suggesting that there has been little, if any, crustal thinning beneath the rift compared to the southeastern edge of the rift. The Poisson’s ratio of 0.27, in combination with the high velocities in the middle and lower crust, indicate that a significant component of the rifted crust has a mafic composition. This finding is important for understanding the occurrence of lower crustal earthquakes in east Africa, because it suggests that at least some of the crust in east Africa could be sufficiently strong at mid- and lower crustal depths to support brittle deformation. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Waveform modeling of historical seismograms of the 1930 Irpinia earthquake provides insight on “blind” faulting in Southern Apennines (Italy)

The Southern Apennines chain is related to the west‐dipping subduction of the Apulian lithosphere. The strongest seismic events mostly occurred in correspondence of the chain axis along normal NW–SE striking faults parallel to the chain axis. These structures are related to mantle wedge upwelling beneath the chain. In the foreland, faulting develops along E–W strike‐slip to oblique‐slip faults related to the roll‐back of the foreland. Similarly to other historical events in Southern Apennines, the I0= XI (MCS intensity scale) 23 July 1930 earthquake occurred between the chain axis and the thrust front without surface faulting. This event produced more than 1400 casualties and extensive damage elongated approximately E‐W. The analysis of the historical waveforms provides the chance to study the fault geometry of this “anomalous” event and allow us to clarify its geodynamic significance. Our results indicate that the MS= 6.6 1930 event nucleated at 14.6 ± 3.06 km depth and ruptured a north dipping, N100°E striking plane with an oblique motion. The fault propagated along the fault strike 32 km to the east at about 2 km/s. The eastern fault tip is located in proximity of the Vulture volcano. The 1930 hypocenter, similarly to the 1990 (MW= 5.8) Southern Apennines event, is within the Mesozoic carbonates of the Apulian foredeep and the rupture developed along a “blind” fault. The 1930 fault kinematics significantly differs from that typical of large Southern Apennines earthquakes, which occur in a distinct seismotectonic domain on late Pleistocene to Holocene outcropping faults. These results stress the role played by pre‐existing, “blind” faults in the Apennines subduction setting.