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Shaded relief map of the Vesuvius volcano with the 16 stations used in the analysis (black triangles). The stations that have names ending with M are the digital ones. Axes dimensions in meters (UTM 33T).
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In this article we apply a passive scattering-imaging method, derived from the method developed by Nishigami (1991) to data from the coda of the local volcano-tectonic (VT) earthquakes of Mt. Vesuvius. This method provides the space distribution of the strong scatterers together with a rough estimate of their strength. In the development of our met...
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Context 1
... of 2,261 local volcano-tectonic (VT) and low-magnitude (local magnitude up to 3.6) events ( Fig. 1) recorded between Jan- uary 1996 and April 2000 by the seismic monitoring network of INGV Naples. VT earthquakes constitute the almost un- ique class of events present in the background seismicity ( Bianco et al., 2005). The recording stations (Fig. 2) were: nine low-dynamic range analog stations whose data are telemetered to the Data Analysis Center (Centro di Sorve- glianza) sampled at 100 samples per second and seven high-dynamic range digital stations with local recording sampled at 125 samples per second. The sensors were 1 Hz Mark Products L4-C vertical component seismometers ...
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Ocean-Solid Earth coupling is the main forcing of generating seismic noise. It has been well known that seismic noise in the frequency band from 0.05 to about 1 Hz results from ocean waves. Components of noise spectrum, also called microseisms, are used to study extreme waves during typhoons. During the KUN-SHEN project (2011-2014), wave measuremen...
Citations
... Differences in scattering characteristics between 3 Hz and higher frequencies are reported in several coda-attenuation imaging studies of volcanoes, especially in the presence of a volcanic edifice (e.g. Tramelli et al. 2009). Nevertheless, an albedo as high as 0.95 had never been measured in volcanoes. ...
In volcanoes, topography, shallow heterogeneity and even shallow morphology can substantially modify seismic coda signals. Coda waves are an essential tool to monitor eruption dynamics and model volcanic structures jointly and independently from velocity anomalies: it is thus fundamental to test their spatial sensitivity to seismic path effects. Here, we apply the Multiple Lapse Time Window Analysis (MLTWA) to measure the relative importance of scattering attenuation vs absorption at Mount St Helens volcano before its 2004 eruption. The results show the characteristic dominance of scattering attenuation in volcanoes at lower frequencies (3-6 Hz), while absorption is the primary attenuation mechanism at 12 and 18 Hz. Scattering attenuation is similar but seismic absorption is one order of magnitude lower than at open-conduit volcanoes, like Etna and Kilauea, a typical behaviour of a (rela-tively) cool magmatic plumbing system. Still, the seismic albedo (measuring the ratio between seismic energy emitted and received from the area) is anomalously high (0.95) at 3 Hz. A radiative-transfer forward model of far-and near-field envelopes confirms this is due to strong near-receiver scattering enhancing anomalous phases in the intermediate and late coda across the 1980 debris avalanche and central crater. Only above this frequency and in the far-field diffusion onsets at late lapse times. The scattering and absorption parameters derived from MLTWA are used as inputs to construct 2-D frequency-dependent bulk sensitivity kernels for the S-wave coda in the multiple-scattering (using the Energy Transport Equations-ETE) and diffusive (AD, independent of MLTWA results) regimes. At 12 Hz, high coda-attenuation anomalies characterize the eastern side of the volcano using both kernels, in spatial correlation with low-velocity anomalies from literature. At 3 Hz, the anomalous albedo, the forward modelling, and the results of the tomographic imaging confirm that shallow heterogeneity beneath the extended 1980 debris-avalanche and crater enhance anomalous intermediate and late coda phases, mapping shallow geological contrasts. We remark the effect this may have on coda-dependent source inversion and tomography, currently used across the world to image and monitor volcanoes. At Mount St Helens, higher frequencies and deep borehole data are necessary to reconstruct deep volcanic structures with coda waves.
... Building of the Scattering model. Similarly to the attenuation models we first used the procedure described by 25,56 and based on the method proposed by 57 . This scattering locator method considers the experimental evidence that the coda energy density can be modelled on a first order with a single isotropic scattering approach. ...
Campi Flegrei caldera (Southern Italy) is a densely inhabited area and suffered several unrest episodes in the last centuries. The dynamic of the caldera is highly debated because of conflicting interpretations. Here we present a detailed reconstruction of the Campi Flegrei structure obtained using the microseismicity recorded during the 1984 unrest. Enhanced Seismic Tomography models obtained with these data allow us describing seismic velocities, attenuation, and scattering patterns. Results show: (1) a plumbing system with a diameter of 1 km located between 2.3 km and 4 km depth (2) a 0.5 km thick caprock located at 2 km depth interpreted as the main structure regulating the fluid interchange between deep and shallow sectors of the caldera, (3) the shape and volume of a shallow reservoir beneath the city of Pozzuoli; this reservoir played a key role during the 1982–1984 unrest, (4) several small reservoirs beneath the main craters of the caldera. All these features fit into the debated question on magmatic or hydrothermal mechanism driving the caldera deformation resulting of crucial importance to allow a better assessment of the hazard.
... Direct P wave energy is measured on the same traces using a fixed window of 1 s in order to avoid contamination with the direct S wave. We calculate the energy density of the direct and coda waves as the sum of the squared filtered time trace and of its Hilbert transform [Wegler and Lühr, 2001;Tramelli et al., 2009]. ...
... Scattering tomography assumes that, in a volume with average scattering power, the strongest scatterers can be approximated as single-scattering regions, producing strong changes in coda envelopes at different lapse times [Nishigami, 1991;Matsumoto et al., 1998;Nishigami, 2000;Tramelli et al., 2006Tramelli et al., , 2009. The scattering power of the blocks constituting a 3-D grid is related in the inversion problem to the ratio between the energy recorded in a 2 s coda time window, n , and corresponding to the location of the nth inhomogeneity (over a total of N) and the average homogeneous energy, (both integrated over time), n ∕ : ...
... As in Tramelli et al. [2009], we assume that the strongest scatterers in a complex heterogeneous medium will produce intensity increases which may be modeled by assuming single scattering. In other words, we extract single-scattering components in a diffusion dominant process. ...
We present a combined 3D P-wave attenuation, 2D S-coda attenuation, and 3D S-coda scattering tomography model of fluid pathways, feeding systems, and sediments below Mount St. Helens (MSH) volcano between depths of 0 and 18 km. High-scattering and high-attenuation shallow anomalies are indicative of magma and fluid-rich zones within and below the volcanic edifice down to 6 km depth, where a high-scattering body outlines the top of deeper aseismic velocity anomalies. Both the volcanic edifice and these structures induce a combination of strong scattering and attenuation on any seismic wave-field, particularly those recorded on the northern and eastern flanks of the volcanic cone. North of the cone between depths of 0 and 10 km a low-velocity, high-scattering, and high-attenuation north–south trending trough is attributed to thick piles of Tertiary marine sediments within the St. Helens Seismic Zone. A laterally-extended 3D scattering contrast at depths of 10 to 14 km is related to the boundary between upper and lower crust, and caused in our interpretation by the large scale interaction of the Siletz terrane with the Cascade arc crust. This contrast presents a low-scattering, 4–6 km2 ”hole” under the north-eastern flank of the volcano. We infer that this section represents the main path of magma ascent from depths greater than 6 km at MSH, with a small north-east shift in the lower plumbing system of the volcano. We conclude that combinations of different non-standard tomographic methods, leading toward full-waveform tomography, represent the future of seismic volcano imaging.
... A number of methods were developed for estimation of intrinsic (Q À1 i ) and scattering (Q À1 s ) attenuation. Some of the most commonly used methods for estimation of relative contribution of these two parameters in coda attenuation were proposed by Wu (1985), Zeng (1991), Hoshiba et al. (1991), Fehler et al. (1992), Mayeda et al. (1992), Wennerberg (1993 and Bianco et al. (2002Bianco et al. ( , 2005 for isotropic scattering and by Hoshiba (1995), Tramelli et al. (2009), De Siena et al. (2009 and Mayeda et al. (2008) for nonisotropic scattering. The multiple scattering models of Gao et al. (1983) and Wu and Aki (1988) and energy flux model of Frankel and Wennerberg (1987) give some insight in the physical interpretation of coda wave quality factor (Q c ) and provide methods of separation of Q i and Q s . ...
... Real volcano structures usually combine depth-dependent velocity gradients, low-velocity regions related to partial melt and/or hydrothermal alterations, and high-velocity regions usually interpreted as chilled magma bodies. On top of this, we must keep in mind the effects produced by the sharp topography of volcanic areas and the presence of strong scatterers and attenuating bodies (Neuberg and Pointer 2000; Martínez-Arévalo et al. 2003 Tramelli et al. 2006 Tramelli et al. , 2009 Métaxian et al. 2009; O'Brien and Bean 2009). Therefore, it is very difficult to estimate precisely what values of azimuth and apparent slowness should be expected for seismic waves propagating in heterogeneous media. ...
We analyse shot data recorded by eight seismic arrays during an active-source seismic experiment carried out at Deception Island (Antarctica) in 2005 January. For each source we estimate the apparent slowness and propagation azimuth of the first wave arrival. Since both source and receiver positions are accurately known, we are able to interpret the results in terms of the effect of the heterogeneities of the medium on wave propagation. The results show the presence of significant propagation anomalies. Nearby shots produce large apparent slowness values above 0.6 s km–1, while distant shots produce small values, down to about 0.15–0.20 s km–1. These values are different for each array, which shows the importance of the local structure under the receiver. The spatial distributions of apparent slowness are not radial as we would expect in a flat-layered medium. And again, these distributions are different for each array. The azimuth anomalies defined as the difference between the empirical estimates and the values expected in a 1-D model (i.e. the source-array directions) suggest ubiquitous wave front distortions. We have detected both positive and negative anomalies. For some shot-array geometries, azimuth anomalies are quite large with values up to 60°. The distribution of the anomalies depends on the position of the array. Some of these features can be interpreted in terms of a shallow magma chamber and shallow rigid bodies imaged by high-resolution seismic tomography. However several details remain unexplained. Further work is required, including modelling of synthetic wavefields on realistic models of Deception Island and/or apparent slowness vector tomography.
... A number of methods were developed for estimation of intrinsic (Q À1 i ) and scattering (Q À1 s ) attenuation. Some of the most commonly used methods for estimation of relative contribution of these two parameters in coda attenuation were proposed by Wu (1985), Zeng (1991), Hoshiba et al. (1991), Fehler et al. (1992), Mayeda et al. (1992), Wennerberg (1993 and Bianco et al. (2002Bianco et al. ( , 2005 for isotropic scattering and by Hoshiba (1995), Tramelli et al. (2009), De Siena et al. (2009 and Mayeda et al. (2008) for nonisotropic scattering. The multiple scattering models of Gao et al. (1983) and Wu and Aki (1988) and energy flux model of Frankel and Wennerberg (1987) give some insight in the physical interpretation of coda wave quality factor (Q c ) and provide methods of separation of Q i and Q s . ...
In this study the S-wave attenuation mechanism is analyzed and intrinsic and scattering attenuation effects are separated. This helps in understanding the physical mechanisms governing attenuation properties of the crust of this region. It has been observed that the Qs−1, Qd−1 and Qc−1 values at all frequencies are comparable. The estimated Le−1, B0, Qi−1, Qs−1, Qd−1 and Qc−1 values show that S-wave attenuation is primarily controlled by scattering attenuation in the source zone of the 1999 Chamoli earthquake. My results also show that for the source zone of 1999 Chamoli earthquake in the Garhwal Himalayas seismic albedo is very high, i.e. attenuation is mainly controlled by scattering attenuation. In conclusion, The extinction length Le varies between about 12 km to about 125 km in the study region. The seismic albedo (B0) values vary between 0.65 and 0.8. B0 values are very large (>0.5) showing that at all frequencies scattering attenuation is the dominating factor causing attenuation of seismic waves. This shows that the degree of heterogeneity is very high for the frequency range considered in this area.
We present a comprehensive review of seismic and gravity observations and tomographic models produced over the past four decades in order to understand the structure of the crust beneath the Campi Flegrei caldera. We describe the main lithological and structural discontinuities defined through these observations, illustrate their geophysical responses, and discuss the constraints they give to the understanding of magmatic and volcanic processes. Micro-seismic crises related to caldera unrest, and ambient seismic noise measurements provide comprehensive seismic data to local earthquake and ambient noise tomography. In combination with reflection data from onshore and offshore active seismic experiments, velocity tomography reconstructs the elastic properties of the caldera between surface and ~4 km depth. Active experiments also define the depth of lithological interfaces and deep (~7.5 km) partially molten bodies. Seismic attenuation tomography provides information complementary to velocity tomography, defining lateral lithological changes and the geometry of onshore and offshore fluid and magma bodies down to 4 km depth. Once compared with seismic analyses, gravity data highlight lateral changes in the offshore caldera structures. During the deformation and seismo-geochemical unrest (1982–1984), they permitted to reconstruct a minor (<1 km lateral extent) melt volume related to the point of maximum uplift measured at the caldera. Seismic coda-wave amplitude inversions depict the caldera rim limits in analogy to velocity tomography and map the lateral extension of ~4-km-deep deformation source. Once combined with the results from velocity tomography and gravity inversions, they reconstruct the feeding systems that connect deep deformation source and shallow vents across the eastern caldera, capped by a seismic horizon around a depth of 2 km.
Two recent hazardous earthquakes ( M 5.8 and 5.5) in southeastern Korea were the largest instrumentally recorded inland events after an abnormally long, seismically quiet, period. In this study, we used coda envelope tomography to observe the heterogeneities related to active faults, which can, in turn, help mitigate seismic hazard in the area. However, this tomography was not able to detect faults in the intraplate region. By separating the periods before and after the M 5.8 earthquake, we analyzed 225 and 204 seismograms obtained from 127 and 86 events, respectively. Both periods showed time-varying heterogeneity correlated with fault activity. Adding 446 seismograms from 235 aftershocks of the two events to the analysis showed us a heterogenous structure that closely correlated to the active faults where the recent earthquakes originated.
Abstract This manuscript shows a new multidisciplinary interpretation approach
of the internal structure of Tenerife island. The central core of this work
is the determination of the three dimensional attenuation structure of the region
using P-waves and the Coda Normalization (CN) method. This study has
been performed using 45303 seismograms recorded in 85 seismic stations from
an active experiment (air-gun shots) conducted in January 2007. The interpretation
of these new results is done combining the new images with previous
studies performed in the area such as seismic velocity tomography, magnetic
structure, magnetotelluric surveys or gravimetric models. Our new 3D images
indicate the presence of seismic attenuation contrasts, with areas of high and
low seismic attenuation patterns. High seismic attenuation zones are observed
both in shallow and deeper areas. The shallowest area of Las Cañadas Caldera
complex (1-3 km thick) is dominated by high attenuation behavior and it is
interpreted as the combined effect of sedimentary and volcanoclastic deposits,
multifracturated systems and the presence of shallow aquifers. At the same
time, the deeper analyzed area, beyond 8 km below sea level, is dominated by
high attenuation pattern and it is interpreted as the consequence of the effect
of high temperature rocks in the crustal-mantle boundary. This interpretation
is compatible and confirmed by previous models that indicate the presence
of underplating magma in this region. On the contrary, some low attenuation
bodies and structures have been identified at different depths. A deep
low attenuation central body is interpreted as the original central structure
associated to the early stage of Tenerife island. At shallower depths, some low
attenuation bodies are compatible with old intermediate magmatic chambers
postulated by petrological studies. Finally, in the North of the island (La Orotava
valley) we can interpreted the low attenuation structure as the headwall
of this valley supporting the idea that Las Cañadas Caldera and this valley
resulted from two different destructive processes.
The Onikobe area is an active geothermal area situated in the Ou backbone range of northeastern Honshu, Japan. It is home to calderas from the Tertiary to Quaternary eras and active volcanoes. A systematic spatial variation of Qc has been found in this area: Qc values are lower at stations in and around calderas than at other stations. The amplitude of coda waves with high Qcs decreases more slowly after a lapse time of around 7–10s than that with low Qcs. In the present study, to determine causes for these coda decay variations, coda envelopes were synthesized in a structure model in which high attenuation zones existed beneath the Onikobe and Sanzugawa calderas and where scattering coefficients were higher in the lower crust than in the upper crust. Using hypocenters shallower than 10 km, envelopes were calculated for 256 station-hypocenter pairs with epicentral distances of less than 10 km. It was assumed that the coda waves were composed of S-S scattered waves, and that the scattering was single and isotropic. The observed features of the Qc distribution were reproduced in the synthesis, and synthesized envelopes were found to mostly coincide with observed decay curves. The top of high attenuation zones was thus estimated as being deeper than 7.5 km. The structure assumed for the synthesis was consistent with that of previous studies. We consider that the structure model used was appropriate, and that high attenuation zones beneath calderas and the reflective lower crust caused the spatial variation of the Qc and decay curves in the Onikobe area. We also consider that studies using coda decay would be beneficial in detecting high attenuation zones and the reflective lower crust.
