A. M.G. Ferreira

• PhD
• Lecturer at University College London

Understanding the signatures and mechanisms of failed volcanic eruptions is vital for mapping magma plumbing systems and forecasting volcanic hazards. Geological structures like fractures and faults are key to guiding magma, but their mechanisms remain unclear due to limited 3-D mapping of faults in volcanic regions and sufficiently precise earthqu...

Surface wave amplification measurements have narrower depth sensitivity when compared to more traditional seismic observables such as surface wave dispersion measurements. In particular, Love wave amplification measurements have the advantage of strong sensitivity to the crust. For the first time, we explore the potential of Love wave amplification...

Seismic anisotropy is key to constrain mantle flow, but it is challenging to image and interpret it. To better understand the robustness of anisotropy tomography, we create a 2-D ridge-to-slab geodynamic model and compute the associated fabrics. Using the resulting 21 elastic constants we compute seismic waveforms, which are inverted for isotropic...

In this work, we describe a framework for solving spherical inverse imaging problems using posterior sampling for full uncertainty quantification. Inverse imaging problems defined on the sphere arise in many fields, including seismology and cosmology where images are defined on the globe and the cosmic sphere, and are generally high-dimensional and...

Uncertainty quantification is a crucial step of cosmological mass-mapping that is often ignored. Suggested methods are typically only approximate or make strong assumptions of Gaussianity of the shear field. Probabilistic sampling methods, such as Markov chain Monte Carlo (MCMC), draw samples form a probability distribution, allowing for full and f...

Deep earthquakes occur down to 700 km depth where pressure is up to two orders of magnitude greater than in the crust. Rupture characteristics and propagation mechanisms under those extreme conditions are still poorly constrained. We invert seismic waveforms for the spatial dimensions, duration and stress drop of deep‐focus earthquakes (Mw 6.7–7.7)...

Inverse problems defined on the sphere arise in many fields, and are generally high-dimensional and computationally very complex. As a result, sampling the posterior of spherical inverse problems is a challenging task. In this work, we describe a framework that leverages a proximal Markov chain Monte Carlo algorithm to efficiently sample the high-d...

Structural fault complexity at depth affects seismic hazard, earthquake physics, and regional tectonic behavior, but constraining such complexity is challenging. We present earthquake source models of the February 21, 2008, Mw 6.0 Wells event that occurred in the Basin and Range in the western USA, suggesting the rupture of both the shallow and dee...

Global tomography models show a large low‐velocity anomaly extending from the core‐mantle boundary (CMB) beneath South Africa to the upper mantle in East Africa. Although it is believed that this anomaly is linked to mantle upwellings that control key surface features of the African continent, its origin and evolution are still debated. Here we ass...

While the downward mass flux in the Earth's deep interior is well constrained by seismic tomography, the upward flux is still poorly understood and debated. Recent tomography studies suggest that we are now starting to resolve deep mantle plume structures. However, a lack of uncertainty quantification impedes a full assessment of their significance...

Determining the crustal structure of ocean island volcanoes is important to understand the formation and tectonic evolution of the oceanic lithosphere and tectonic swells in marine settings, and to assess seismic hazard in the islands. The Azores Archipelago is located near a triple junction system and is possibly under the influence of a mantle pl...

Recent seismic studies indicate the presence of seismic anisotropy near subducted slabs in the transition zone and uppermost lower mantle (mid-mantle). In this study we investigate the origin of radial anisotropy in the mid-mantle using 3-D geodynamic subduction models combined with mantle fabric simulations. These calculations are compared with se...

We build SWUS-amp, a three-dimensional shear-wave speed model of the uppermost mantle of the western U.S. using Rayleigh wave amplification measurements in the period range of 35–125 s from teleseismic earthquakes. This represents the first-ever attempt to invert for velocity structures using Rayleigh wave amplification data alone. We use over 350,...

For ice concentrations less than 85%, internal ice stresses in the sea ice pack are small and sea ice is said to be in free drift. The sea ice drift is then the result of a balance between Coriolis acceleration and stresses from the ocean and atmosphere. We investigate sea ice drift using data from individual drifting buoys as well as Arctic‐wide g...

We present a new inversion method for modelling multiple fault sources combining seismic and geodetic data. The technique takes into account 3-D Earth structure in the modelling and uses a Monte Carlo inversion scheme that extensively explores the parameter space, which enables the assessment of source parameter uncertainties. Eleven parameters are...

We present a new inversion method for modelling multiple fault sources combining seismic and geodetic data. The technique takes into account 3-D Earth structure in the modelling and uses a Monte Carlo inversion scheme that extensively explores the parameter space, which enables the assessment of source parameter uncertainties. Eleven parameters are...

Seismic anisotropy provides key information to map the trajectories of mantle flow and understand the evolution of our planet. While the presence of anisotropy in the uppermost mantle is well established, the existence and nature of anisotropy in the transition zone and uppermost lower mantle are still debated. Here we use three-dimensional global...

We examine the patterns of radial anisotropy in global tomography images of the mantle transition zone near subducted slabs in the western Pacific. Fast SV velocity anomalies are observed in this region, which are compatible with anisotropy due to lattice-preferred orientation in wadsleyite. Using mineral physics reports of the dependency of the st...

Several theoretical studies indicate that a substantial fraction of the measured seismic anisotropy could be interpreted as extrinsic anisotropy associated with compositional layering in rocks, reducing the significance of strain‐induced intrinsic anisotropy. Here we quantify the potential contribution of grain‐scale and rock‐scale compositional an...

Supporting Information S1

We develop a new method for measuring ellipticity of Rayleigh waves from ambient noise records by degree-of-polarization (DOP) analysis. The new method, named DOPE , shows a good capability to retrieve accurate ellipticity curves separated from incoherent noise. In order to validate the method we perform synthetic tests simulating noise in a 1D Ear...

Source models of mid-oceanic earthquakes are often based only on far-field, teleseismic data. The uncertainties of all source parameters are rarely quantified, which restricts our understanding of how these events slip and how oceanic lithosphere is formed. Here, we perform moment tensor inversions for five Mw 4.6–5.9 earthquakes that occurred in t...

Supporting Information S1

Observations of shear wave anisotropy are key for understanding the mineralogical structure and flow in the mantle. Several researchers have reported the presence of seismic anisotropy in the lowermost 150-250 km of the mantle (i.e., D '' layer), based on differences in the arrival times of vertically (SV) and horizontally (SH) polarized shear w...

Up until now, Portugal lacked a countrywide shear velocity model sampling short length-scale crustal structure, which limits interpretations of seismicity and tectonics, and predictions of strong ground motion. In turn, such interpretations and predictions are important to help mitigate risk of destruction from future large on- and offshore earthqu...

Observed seismic anisotropy gives the most direct information on mantle flow, but it is challenging to image it robustly at global scales. Difficulties in separating crustal from mantle structures in particular can have a strong influence on the imaging. Here we carry out several resolution tests using both real and synthetic data, which show that...

Northern Italy is a diverse geological region, including the wide and thick Po Plain sedimentary basin, which is bounded by the Alps and the Apennines. The seismically slow shallow structure of the Po Plain is difficult to retrieve with classical seismic measurements such as surface wave dispersion, yet the detailed structure of the region greatly...

Observed seismic anisotropy gives the most direct information on mantle flow, but it is challenging to image it robustly at global scales. Difficulties in separating crustal from mantle structures in particular can have a strong influence on the imaging. Here we carry out several resolution tests using both real and synthetic data, which show that...

We apply a new method to build receiver-side amplification maps from the amplitude of surface waves recorded at nearby stations. From these maps, we extract single-station amplification dispersion curves that are subsequently inverted to retrieve the 1-D structure below each receiver using a neighbourhood algorithm approach. The technique is applie...

Resolving robustly source parameters of small-moderate magnitude earthquakes is still a challenge in seismology. We infer directivity from apparent source time functions (ASTFs) at regional distance and quantify the associated uncertainties. ASTFs are used for: (i) modeling a propagating 1D line source from the duration data; and, (ii) inverting th...

We measure ellipticity of teleseismic Rayleigh waves at 95 seismic stations in Northern Italy, for wave period between 10 and 110 s, using an automatic technique and a large volume of high-quality seismic recordings from over 500 global earthquakes that occurred in 2008– 2014. Northern Italy includes a wide range of crustal structures, from the wid...

The surface wave full ray theory (FRT) is an efficient tool to calculate synthetic waveforms of surface waves. It combines the concept of local modes with exact ray tracing as a function of frequency, providing a more complete description of surface wave propagation than the widely used great circle approximation (GCA). The purpose of this study is...

Mantle plumes are thought to play a key role in transferring heat from the core-mantle boundary to the lithosphere, where it can significantly influence plate tectonics. On impinging on the lithosphere at spreading ridges or in intra-plate settings, mantle plumes may generate hotspots, large igneous provinces and hence considerable dynamic topograp...

We analyse the elastic wave propagation phenomena in the presence of micro-structure. More precisely, we study 1D seismic wave propagation in micropolar elastic media. Micropolar medium is a generalization of classical elastic medium, where each particle has intrinsic rotational degrees of freedom (spin). We give a physical interpretation of the mi...

Seismic ambient noise tomography is applied to central and southern Mozambique, located in the tip of the East African Rift (EAR). The deployment of MOZART seismic network, with a total of 30 broad-band stations continuously recording for 26 months, allowed us to carry out the first tomographic study of the crust under this region, which until now...

The surface wave full ray theory (FRT) is an efficient tool to calculate synthetic waveforms of surface waves. It combines the concept of local modes with exact ray tracing as a function of frequency, providing a more complete description of surface wave propagation than the widely used great circle approximation (GCA). The purpose of this study is...

We apply a new technique to retrieve local amplification from the amplitude of seismic surface waves, in various areas on Earth covered by dense seismic arrays. By taking the ratio of amplitudes measured at two close-by locations, and by averaging over many recordings, we are able to isolate the receiver-side contribution from the effects of struct...

Mantle plumes play an efficient role in transferring heat from the core-mantle boundary to the surface, where they significantly influence plate tectonics. It is well known that, upon impinging on the lithosphere at spreading ridges or intra-oceanic settings, mantle plumes generate hotspots, Large Igneous Provinces and considerable dynamic topograp...

The amplitude ratio between horizontal and vertical components of Rayleigh waves (also known as ellipticity) is in principle uniquely sensitive to local earth structure beneath each recording station. Rayleigh wave ellipticity is mostly influenced by the shallowest layers, so it can be effectively used to infer the structure of the uppermost crust,...

Comparisons between earthquake source parameters as determined by InSAR and the global centroid moment tensor (GCMT) catalogue show discrepancies between locations derived using these independent methods (Ferreira et al., 2011; Weston et al., 2011, 2012). Earthquake centroid location determination using InSAR data (named the ‘InSAR Centroid Moment...

We present a new global whole-mantle model of isotropic and radially anisotropic S velocity structure (SGLOBE-rani) based on ~43,000,000 surface-wave and ~420,000 bodywave travel time measurements, which is expanded in spherical harmonic basis functions up to degree 35. We incorporate crustal thickness perturbations as model parameters in the inver...

It has been observed that vertically (SV) and horizontally (SH) polarised S waves crossing the lowermost mantle sometimes are split by a few seconds The splitting of such waves is often interpreted in terms of seismic anisotropy in the D” region. Here we investigate systematically the effects of elastic, anelastic, isotropic and anisotropic structu...

Non-uniqueness for extended fault slip inversions is well-known and current efforts are focused on assessing and understanding the uncertainties. These ambiguities can be explored through Popperian falsification, where trial models either become members of the solution ensemble or are falsified resulting due to a large data misfit. Classification o...

While the first-order Born approximation is increasingly being used in many seismic tomography efforts, its domain of validity to forward model seismic waveforms has not been quantified in the context of current 3-D earth models yet. We here address this issue by comparing teleseismic synthetic surface waveforms calculated using the Born approximat...

Inversions for the full slip distribution of earthquakes provide detailed models of earthquake sources, but stability and non-uniqueness of the inversions is a major concern. The problem is underdetermined in any realistic setting, and significantly different slip distributions may translate to fairly similar seismograms. In such circumstances, inv...

S U M M A R Y We present spectra concentrating on the lowest-frequency normal modes of the Earth obtained from records of the invar-wire strainmeters and STS-1 broad-band seismometers located in the Black Forest Observatory, Germany after the disastrous earthquakes off the NW coast of Sumatra in 2004 and off the coast near Tohoku, Japan in 2011. We...

We present observations of cross coupled spheroidal modes in the Earth's free oscillation spectrum recorded by the vertical component G-ring laser (Geodetical Station Wettzell) of the 2011 Mw 9.0 Tohoku-Oki earthquake. In an attempt to determine which are the mechanisms responsible for spheroidal energy in a vertical axes rotational spectra, we fir...

J.A. López-Comino, D. Stich, A.M.G. Ferreira, J. Morales

We present a new global whole‐mantle model of isotropic and radially anisotropic S velocity structure (SGLOBE‐rani) based on ~43,000,000 surface wave and ~420,000 body wave travel time measurements, which is expanded in spherical harmonic basis functions up to degree 35. We incorporate crustal thickness perturbations as model parameters in the inve...

José Ángel López Comino, Daniel Stich, José Morales Soto, and Ana M. G. Ferreira

Seismic tomography is a powerful tool to decipher the Earth's interior structure at various scales. Traveltimes of seismic waves are widely used to build velocity models, whereas amplitudes are still only seldomly accounted for. This mainly results from our limited ability to separate the various physical effects responsible for observed amplitude...

We present a new earthquake source inversion technique based on normal mode data for the simultaneous determination of the rupture duration, length and moment tensor of large earthquakes with unilateral rupture. We use ultra low-frequency (f < 1 mHz) mode singlets and multiplets which are modelled using Higher Order Perturbation Theory (HOPT), taki...

A joint earthquake source inversion technique is presented that uses InSAR and long-period teleseismic data, and, for the first time, takes 3-D Earth structure into account when modelling seismic surface and body waves. Ten average source parameters (Moment, latitude, longitude, depth, strike, dip, rake, length, width and slip) are estimated; hence...

Since the 1960s seismologists have mapped anisotropy in the uppermost mantle, the mantle transition zone, and the D” region. When combined with constraints from mineral physics and geodynamics, anisotropy provides critical information on the geometry of mantle flow. Here we review the theory, early work, recent tomographic models, and experimental...

Rapid and accurate source characterizations of large, shallow subduction earthquakes are key for improved tsunami warning efforts. We assess the quality of source parameters of large magnitude (Mw ≥ 7.5) shallow subduction earthquakes of the past 20 yr determined using SCARDEC, a recent fully automated broad-band body-wave source inversion techniqu...

Gareth J. Funning, Ana M. Ferreira, Jennifer M. Weston, and Hannah Bloomfield

Project MOZART (MOZAmbique Rift Tomography) aims to investigate the geological structure and current tectonic activity of the Mozambique sector of the East African Rift System (EARS). Space geodesy has indicated in recent years that the border between Nubia and the Somalian plate at these latitudes (16°S to 24°S) encompasses the Rovuma microplate,...

In this study, we explore the potential of measuring systematically the Earth's free oscillations using ring laser gyro (RLG) vertical axis rotational records. The RLG that we use is the vertical axis G-ring laser system of the Geodetic Observatory Wettzell (Germany). In 2009, its signal-to-noise ratio was considerably improved over the broadband f...

Rotational seismology is a recent and promising field in active development that focuses on the study of all aspects concerning rotational ground motions induced by earthquakes, explosions, and ambient vibrations among others. The understanding of rotational ground motions is relevant to several disciplines: seismology, earthquake engineering, explo...

Progress in seismology led to numerous earthquake catalogues, which routinely report source models. However, evaluating the quality of reported source parameters is difficult, due to the general lack of benchmark solutions. Ongoing efforts in satellite geodesy can help us tackle these issues, as they provide an independent way of characterizing ear...

We use normal mode singlets of ultra-long period spheroidal modes (below 1 mHz) to determine the spatio-temporal characteristics (rupture time and length) of large magnitude earthquakes. We have set up an inversion scheme to calculate the phase differences, called the initial phases, between finite source singlets and point source singlets calculat...

Robust earthquake source parameters (e.g., location, seismic moment, fault geometry) are essential for reliable seismic hazard assessment and the investigation of large-scale tectonics. They are routinely estimated using a variety of data and techniques, such as seismic data and, more recently, Interferometric Synthetic Aperture Radar (InSAR). Comp...

Seismic data are routinely used to determine source models for earthquakes and, increasingly, Interferometric Synthetic Aperture Radar (InSAR) data are also being used. Each dataset has its own strengths and weaknesses which complement each other when jointly inverted. A recent systematic comparison between InSAR and seismically-determined source p...

Earthquake source models are routinely determined using seismic data and are reported in many seismic catalogues, such as the Global Centroid Moment Tensor (GCMT) catalogue. Recent advances in space geodesy, such as InSAR, have enabled the estimation of earthquake source parameters from the measurement of deformation of the Earth's surface, indepen...

We test and compare source parameters for the major (Mw≥7.8) subduction earthquakes of the past 20 years obtained using two different methods. Specifically, we compare the quality of the GCMT (Global Centroid Moment Tensor) method with that of the SCARDEC method (Seismic source ChAracteristics Retrieved from DEConvolving teleseismic body waves), wh...

We report for the first time observations of Earth's toroidal free oscillations recorded on a ring laser system that is sensitive to rotational ground motions around a vertical axis. Because of the high noise level on the horizontal translational components in classical seismometers, long-period toroidal modes are amongst the most challenging obser...