scholarly journals Inside Mt. Vesuvius: a new method to look at the seismic (velocity and attenuation) tomographic imaging

2013 ◽  
Vol 56 (4) ◽  
Author(s):  
Edoardo Del Pezzo ◽  
Francesca Bianco
Keyword(s):  
Graphical Representation ◽  
Seismic Velocity ◽  
P Wave ◽  
Low Velocity ◽  
Geological Structures ◽  
High Attenuation ◽  
Amplitude Spectra ◽  
Vertical Slice ◽  
3D Volume ◽  
Color Scales

<p>New velocity and attenuation images of the geological structures below Mt. Vesuvius have been obtained using the programming facilities as well as the enhanced graphical power of Mathematica<span><sup>8TM</sup></span>. The velocity and attenuation space distributions, already calculated inverting respectively P-wave travel times and amplitude spectra of local VT quakes, are first optimally interpolated and then graphically represented in a new Mathematica<span><sup>8TM</sup></span> code notebook (a powerful computational document with more facilities than a simple code) developed by the present authors. The notebook aims at interactively and friendly representing 3D volume distributions of velocity and attenuation parameters. The user can easily obtain vertical sections (N-S, E-W, NE-SW and NW-SE oriented) and define color scales to represent velocity or attenuation variations or prefer iso-surface plots to represent the pattern of peculiar geological structures. The use of dynamic graphical representation, allowing the sliding of any (horizontal and/or vertical) slice through the volume under study, gives an unusual and powerful vision of any small velocity or attenuation anomaly. The (open source) code, coupled with the friendly use of internal routines of Mathematica, allows to adapt the graphical representation to any user necessity. The method appears to be particularly adapt to represent attenuation images, where the space variations of the parameters are strong with respect to their average. The 3-D plots of the interpolated velocity and attenuation fields enhance the image of Mt. Vesuvius structure, evidencing low-velocity associated with high attenuation anomalies which appeared unfocused in the plots reported by Scarpa et al. [2002] and De Siena et al. [2009].</p>

scholarly journals New insights into Mt. Vesuvius hydrothermal system and its dynamic based on a critical review of seismic tomography and geochemical features

2013 ◽  
Vol 56 (4) ◽  
Author(s):  
Edoardo Del Pezzo ◽  
Giovanni Chiodini ◽  
Stefano Caliro ◽  
Francesca Bianco ◽  
Rosario Avino
Keyword(s):  
Hydrothermal System ◽  
Seismic Velocity ◽  
Seismic Energy ◽  
P Wave ◽  
Depth Range ◽  
Low Velocity ◽  
High Attenuation ◽  
Amplitude Spectra ◽  
Wave Travel ◽  
Attenuation Values

<p>The seismic velocity and attenuation tomography images, calculated inverting respectively P-wave travel times and amplitude spectra of local VT quakes at Mt. Vesuvius have been reviewed and graphically represented using a new software recently developed using Mathematica<span><sup>8TM</sup></span>. The 3-D plots of the interpolated velocity and attenuation fields obtained through this software evidence low-velocity volumes associated with high attenuation anomalies in the depth range from about 1 km to 3 km below the sea level. The heterogeneity in the distribution of the velocity and attenuation values increases in the volume centred around the crater axis and laterally extended about 4 km, where the geochemical interpretation of the data from fumarole emissions reveals the presence of a hydrothermal system with temperatures as high as 400-450°C roughly in the same depth range (1.5 km to 4 km). The zone where the hydrothermal system is space-confined possibly hosted the residual magma erupted by Mt. Vesuvius during the recent eruptions, and is the site where most of the seismic energy release has occurred since the last 1944 eruption.</p>

Crosswell seismic imaging in a contaminated basalt aquifer

Geophysics ◽  
2004 ◽  
Vol 69 (1) ◽  
pp. 16-24 ◽  
Author(s):  
Thomas M. Daley ◽  
Ernest L. Majer ◽  
John E. Peterson
Keyword(s):  
Seismic Source ◽  
P Wave ◽  
Low Velocity ◽  
S Waves ◽  
High Attenuation ◽  
Well Spacing ◽  
Simultaneous Acquisition ◽  
Environmental Laboratory ◽  
New Type ◽  
Borehole Seismic

Multiple seismic crosswell surveys have been acquired and analyzed in a fractured basalt aquifer at Idaho National Engineering and Environmental Laboratory. Most of these surveys used a high‐frequency (1000–10,000 Hz) piezoelectric seismic source to obtain P‐wave velocity tomograms. The P‐wave velocities range from less than 3200 m/s to more than 5000 m/s. Additionally, a new type of borehole seismic source was deployed as part of the subsurface characterization program at this contaminated groundwater site. This source, known as an orbital vibrator, allows simultaneous acquisition of P‐ and S‐waves at frequencies of 100 to 400 Hz, and acquisition over larger distances. The velocity tomograms show a relationship to contaminant transport in the groundwater; zones of high contaminant concentration are coincident with zones of low velocity and high attenuation and are interpreted to be fracture zones at the boundaries between basalt flows. The orbital vibrator data show high Vp/Vs values, from 1.8 to 2.8. In spite of the lower resolution of orbital vibrator data, these data were sufficient for constraining hydrologic models at this site while achieving imaging over large interwell distances. The combination of piezoelectric data for closer well spacing and orbital vibrator data for larger well spacings has provided optimal imaging capability and has been instrumental in our understanding of the site aquifer's hydrologic properties and its scale of heterogeneity.

Seismic structure of basalt flows from surface seismic data, borehole measurements, and synthetic seismogram modeling

Geophysics ◽  
2001 ◽  
Vol 66 (6) ◽  
pp. 1925-1936 ◽  
Author(s):  
Moritz M. Fliedner ◽  
Robert S. White
Keyword(s):  
Velocity Structure ◽  
Seismic Velocity ◽  
Synthetic Seismogram ◽  
P Wave ◽  
Wide Angle ◽  
Seismic Velocities ◽  
Seismic Structure ◽  
Low Velocity ◽  
Amplitude Variation With Offset ◽  
Velocity Gradients

We use the wide‐angle wavefield to constrain estimates of the seismic velocity and thickness of basalt flows overlying sediments. Wide angle means the seismic wavefield recorded at offsets beyond the emergence of the direct wave. This wide‐angle wavefield contains arrivals that are returned from within and below the basalt flows, including the diving wave through the basalts as the first arrival and P‐wave reflections from the base of the basalts and from subbasalt structures. The velocity structure of basalt flows can be determined to first order from traveltime information by ray tracing the basalt turning rays and the wide‐angle base‐basalt reflection. This can be refined by using the amplitude variation with offset (AVO) of the basalt diving wave. Synthetic seismogram models with varying flow thicknesses and velocity gradients demonstrate the sensitivity to the velocity structure of the basalt diving wave and of reflections from the base of the basalt layer and below. The diving‐wave amplitudes of the models containing velocity gradients show a local amplitude minimum followed by a maximum at a greater range if the basalt thickness exceeds one wavelength and beyond that an exponential amplitude decay. The offset at which the maximum occurs can be used to determine the basalt thickness. The velocity gradient within the basalt can be determined from the slope of the exponential amplitude decay. The amplitudes of subbasalt reflections can be used to determine seismic velocities of the overburden and the impedance contrast at the reflector. Combining wide‐angle traveltimes and amplitudes of the basalt diving wave and subbasalt reflections enables us to obtain a more detailed velocity profile than is possible with the NMO velocities of small‐offset reflections. This paper concentrates on the subbasalt problem, but the results are more generally applicable to situations where high‐velocity bodies overlie a low‐velocity target, such as subsalt structures.

Crustal Structure and Earthquakes beneath the Jammu and Kashmir Himalaya

2020 ◽  
Author(s):  
Supriyo Mitra ◽  
Swati Sharma ◽  
Debarchan Powali ◽  
Keith Priestley ◽  
Sunil Wanchoo
Keyword(s):  
Seismic Velocity ◽  
Receiver Function ◽  
Joint Inversion ◽  
P Wave ◽  
Kashmir Valley ◽  
Low Velocity ◽  
Surface Wave Dispersion ◽  
Jammu And Kashmir ◽  
Moderate Earthquake ◽  
Tethyan Himalaya

&lt;p align=&quot;justify&quot;&gt;&lt;span&gt;We use P-wave receiver function (P-RF) analysis of broadband teleseismic data recorded at twenty two stations spanning the Jammu-Kishtwar Himalaya, Pir Panjal Ranges, Kashmir Valley, and Zanskar Ranges in Northwest Himalaya to model the seismic velocity structures of the crust and the uppermost mantle. Our network extends from the Shiwalik Himalaya (S) to the Tethyan Himalaya (N), across the major Himalayan thrust systems and litho-tectonic units. We perform Vp/Vs-Depth stacking of P-RF and joint inversion with surface wave dispersion data. Our analysis show that the underthrust Indian crust, beneath the Jammu-Kishtwar Himalaya, has an average thickness of ~40 km and dips northward at ~7-9&amp;#186;. The overlying Himalayan wedge increases in thickness northward from the Shiwalik Himalaya (~8&amp;#8211;10 km) to the Tethyan Himalaya (~25&amp;#8211;30 km). The underthrust Indian crust Moho is marked by a large positive impedance contrast and lies at a depth of ~45 km beneath the Shiwalik Himalaya and ~65 km beneath the Higher Himalaya, deepening northward beneath the Tethyan Himalaya. We observe Moho flexure across the Mandli-Kishanpur Thrust (MKT), in the Shiwalik Himalaya, and beneath the Kishtwar window. Each time to Moho deepens by ~10 km, from ~45 km to ~55 km, and from ~55 km to ~65 km, respectively. The Moho is remarkably flat at ~56 km beneath the Pir Panjal Ranges, from its southern foothills to the northern flank in the Kashmir Valley. North of the Kashmir Valley the Moho dips steeply underneath the Zanskar Ranges from ~56 km to ~62 km. Along the Jammu-Kishtwar common conversion point (CCP) profile the Main Himalayan Thrust (MHT) is highlighted by the low velocity layer (LVL) at a depth of ~8 km beneath the Shiwalik Himalaya to ~25 km beneath the Higher Himalaya. The average dip on the MHT is ~9&amp;#186; and has a frontal ramp beneath the Kishtwar window. The MKT, MBT and MCT are marked by LVLs which splays updip from the MHT. Average crustal Vp/Vs shows that beneath the Shiwalik Himalaya, west of the MFT anticline the crust is mafic in nature while towards the east the crust is felsic in nature. Beneath the Lesser Himalaya the crust is largely felsic, while beneath the Pir Panjal range the crust is intermediate to mafic. North of the Kashmir Valley, beneath the Zanskar range the crust is felsic to intermediate in nature. We compare the source mechanism of the 2013 Kishtwar earthquake (Mw 5.7) and hypocentral location of small-to-moderate earthquake beneath Kishtwar region with the CCP profile. Our results show that these earthquakes occurred on or above the MHT in the unlocking zone, between the frictionally locked shallow segment and deeper creeping segment of the MHT. This marks the zone of stress build-up on the MHT in the interseismic period and is possibly the zone of megathrust initiation.&lt;/span&gt;&lt;/p&gt;

Seismic velocity models for heat zones in Athabasca tar sands

Geophysics ◽  
1990 ◽  
Vol 55 (8) ◽  
pp. 1108-1112 ◽  
Author(s):  
Larry R. Lines ◽  
Ronald Jackson ◽  
James D. Covey
Keyword(s):  
Seismic Velocity ◽  
Three Dimensional ◽  
Velocity Model ◽  
Steam Injection ◽  
P Wave ◽  
Injection Velocity ◽  
Low Velocity ◽  
Borehole Data ◽  
Tar Sands ◽  
Velocity Models

Recent laboratory and field studies indicate that the P-wave velocity in Athabasca tar sands decreases when temperature increases during steam injection. In this paper we derive time variant velocity models from seismic traveltime inversions of both reflection and borehole data. Prior to steam injection, three‐dimensional (3-D) reflector velocity‐depth models are established using image‐ray conversions of traveltimes to depth. The changes in velocity due to steam injection are modeled by inverting traveltime data from seismic monitor surveys after steam injection and comparing these results to velocities computed prior to steam injection. Velocity models are essentially determined by traveltimes from the 3-D seismic reflection survey. The surface‐to‐wellbore data traveltimes show the expected delay caused by steam injection but do not significantly alter the velocity model produced by reflection traveltimes. For seismic monitor surveys, low‐velocity zones show a very good correlation with zones of temperature increase at injector well positions. The results indicate that velocity models obtained from seismic traveltimes may prove useful in detecting steam fronts in tar sands.

scholarly journals Fault-zone waves observed at the southern Joshua Tree earthquake rupture zone

1994 ◽  
Vol 84 (3) ◽  
pp. 761-767
Author(s):  
S. E. Hough ◽  
Y. Ben-Zion ◽  
P. Leary
Keyword(s):  
Fault Zone ◽  
Wave Train ◽  
Spectral Characteristics ◽  
P Wave ◽  
S Wave ◽  
Low Velocity ◽  
Zone Structure ◽  
High Attenuation ◽  
Vertical Fault ◽  
Synthetic Waveform

Abstract Waveform and spectral characteristics of several aftershocks of the M 6.1 22 April 1992 Joshua Tree earthquake recorded at stations just north of the Indio Hills in the Coachella Valley can be interpreted in terms of waves propagating within narrow, low-velocity, high-attenuation, vertical zones. Evidence for our interpretation consists of: (1) emergent P arrivals prior to and opposite in polarity to the impulsive direct phase; these arrivals can be modeled as headwaves indicative of a transfault velocity contrast; (2) spectral peaks in the S wave train that can be interpreted as internally reflected, low-velocity fault-zone wave energy; and (3) spatial selectivity of event-station pairs at which these data are observed, suggesting a long, narrow geologic structure. The observed waveforms are modeled using the analytical solution of Ben-Zion and Aki (1990) for a plane-parallel layered fault-zone structure. Synthetic waveform fits to the observed data indicate the presence of NS-trending vertical fault-zone layers characterized by a thickness of 50 to 100 m, a velocity decrease of 10 to 15% relative to the surrounding rock, and a P-wave quality factor in the range 25 to 50.

Delineation of a low‐velocity body under the Roosevelt Hot Springs geothermal area, Utah, using teleseismic P‐wave data

Geophysics ◽  
1981 ◽  
Vol 46 (10) ◽  
pp. 1456-1466 ◽  
Author(s):  
Russell Robinson ◽  
H. M. Iyer
Keyword(s):  
Hot Springs ◽  
Velocity Structure ◽  
P Wave ◽  
Wave Form ◽  
Geothermal Area ◽  
Uppermost Mantle ◽  
Low Velocity ◽  
Near Surface ◽  
High Attenuation ◽  
Partial Melt

To assess the nature of the heat source associated with the Roosevelt Hot Springs geothermal area, we have investigated the P‐wave velocity structure of the crust and uppermost mantle in the vicinity of the Mineral Mountains, southwest Utah, a region of late Cenozoic rhyolitic and basaltic volcanic activity. A roughly square (30 × 30 km) array of 15 seismographs, centered on the mountains, was operated for a period of 46 days, during which 72 teleseismic events were recorded with sufficient quality for calculation of P‐wave traveltime residuals. Relative residuals, using the array average for each event as reference, show a clear pattern of azimuthal variation of up to 0.3 sec. This pattern implies the existence of a localized region of relatively low‐velocity material extending up from the upper mantle to depths of about 5 km under the Mineral Mountains. A three‐dimensional (3-D) inversion of the data confirms this conclusion and yields a model featuring a region of low velocity (5 to 7 percent less than the surrounding rock) centered under the geothermal area and extending from about 5-km depth down into the uppermost mantle. The near‐surface velocities obtained in the inversion clearly reveal the structure of the region, part of the Basin and Range province. An azimuthally changing pattern of wave‐form distortion, restricted to the central Mineral Mountains, indicates the presence of a small but intensely anomalous region of low velocity and high attenuation at depths of about 15 km. Although we cannot rule out an explanation for the low velocity purely in terms of compositional changes, in view of the geothermal and volcanic manifestations found in the region we prefer an explanation in terms of abnormally high temperature and a small fraction of partial melt. A partial melt model implies a much greater heat reservoir than does a model involving only circulation along deep fault zones.

Integration of Multi-geophysical Approaches to Identify Potential Pathways of Heavy Metals Contamination - A Case Study in Zeida, Morocco

2020 ◽  
Vol 25 (3) ◽  
pp. 415-423
Author(s):  
Ahmed Lachhab ◽  
El Mehdi Benyassine ◽  
Mohamed Rouai ◽  
Abdelilah Dekayir ◽  
Jean C. Parisot ◽  
...  
Keyword(s):  
Heavy Metals ◽  
Seismic Velocity ◽  
Seismic Refraction ◽  
Geophysical Methods ◽  
Low Frequency ◽  
Electrical Current ◽  
P Wave ◽  
Low Resistivity ◽  
Refraction Tomography ◽  
Geophysical Surveys

The tailings of Zeida's abandoned mine are found near the city of Midelt, in the middle of the high Moulouya watershed between the Middle and the High Atlas of Morocco. The tailings occupy an area of about 100 ha and are stored either in large mining pit lakes with clay-marl substratum or directly on a heavily fractured granite bedrock. The high contents of lead and arsenic in these tailings have transformed them into sources of pollution that disperse by wind, runoff, and seepage to the aquifer through faults and fractures. In this work, the main goal is to identify the pathways of contaminated water with heavy metals and arsenic to the local aquifers, water ponds, and Moulouya River. For this reason, geophysical surveys including electrical resistivity tomography (ERT), seismic refraction tomography (SRT) and very low-frequency electromagnetic (VLF-EM) methods were carried out over the tailings, and directly on the substratum outside the tailings. The result obtained from combining these methods has shown that pollutants were funneled through fractures, faults, and subsurface paleochannels and contaminated the hydrological system connecting groundwater, ponds, and the river. The ERT profiles have successfully shown the location of fractures, some of which extend throughout the upper formation to depths reaching the granite. The ERT was not successful in identifying fractures directly beneath the tailings due to their low resistivity which inhibits electrical current from propagating deeper. The seismic refraction surveys have provided valuable details on the local geology, and clearly identified the thickness of the tailings and explicitly marked the boundary between the Triassic formation and the granite. It also aided in the identification of paleochannels. The tailings materials were easily identified by both their low resistivity and low P-wave velocity values. Also, both resistivity and seismic velocity values rapidly increased beneath the tailings due to the compaction of the material and lack of moisture and have proven to be effective in identifying the upper limit of the granite. Faults were found to lie along the bottom of paleochannels, which suggest that the locations of these channels were caused by these same faults. The VLF-EM surveys have shown tilt angle anomalies over fractured areas which were also evinced by low resistivity area in ERT profiles. Finally, this study showed that the three geophysical methods were complementary and in good agreement in revealing the pathways of contamination from the tailings to the local aquifer, nearby ponds and Moulouya River.

The relationship between Vs, Vp, density and depth based on PS-logging data at K-NET and KiK-net sites

2021 ◽  
Author(s):  
Fumiaki Nagashima ◽  
Hiroshi Kawase
Keyword(s):  
Standard Deviation ◽  
Seismic Velocity ◽  
Saturated Soil ◽  
P Wave ◽  
Soil Types ◽  
Depth Range ◽  
Velocity Inversion ◽  
Velocity Models ◽  
Regression Curves ◽  
Ps Logging

Summary P-wave velocity (Vp) is an important parameter for constructing seismic velocity models of the subsurface structures by using microtremors and earthquake ground motions or any other geophysical exploration data. In order to reflect the ground survey information in Japan to the Vp structure, we investigated the relationships among Vs, Vp, and depth by using PS-logging data at all K-NET and KiK-net sites. Vp values are concentrated at around 500 m/s and 1,500 m/s when Vs is lower than 1,000 m/s, where these concentrated areas show two distinctive characteristics of unsaturated and saturated soil, respectively. Many Vp values in the layer shallower than 4 m are around 500 m/s, which suggests the dominance of unsaturated soil, while many Vp values in the layer deeper than 4 m are larger than 1,500 m/s, which suggests the dominance of saturated soil there. We also investigated those relationships for different soil types at K-NET sites. Although each soil type has its own depth range, all soil types show similar relationships among Vs, Vp, and depth. Then, considering the depth profile of Vp, we divided the dataset into two by the depth, which is shallower or deeper than 4 m, and calculated the geometrical mean of Vp and the geometrical standard deviation in every Vs bins of 200 m/s. Finally, we obtained the regression curves for the average and standard deviation of Vp estimated from Vs to get the Vp conversion functions from Vs, which can be applied to a wide Vs range. We also obtained the regression curves for two datasets with Vp lower and higher than 1,200 m/s. These regression curves can be applied when the groundwater level is known. In addition, we obtained the regression curves for density from Vs or Vp. An example of the application for those relationships in the velocity inversion is shown.

scholarly journals Characteristics of relocated hypocenters of the 2018 M6.7 Hokkaido Eastern Iburi earthquake and its aftershocks with a three-dimensional seismic velocity structure

2019 ◽  
Vol 71 (1) ◽  
Author(s):  
Saeko Kita
Keyword(s):  
Seismic Velocity ◽  
Three Dimensional ◽  
Double Difference ◽  
Earthquake Catalog ◽  
Seismic Structure ◽  
Depth Limit ◽  
High Attenuation ◽  
South Central ◽  
Collision Zone ◽  
Hidaka Collision Zone

AbstractI relocated the hypocenters of the 2018 M6.7 Hokkaido Eastern Iburi earthquake and its surrounding area, using a three-dimensional seismic structure, the double-difference relocation method, and the JMA earthquake catalog. After relocation, the focal depth of the mainshock became 35.4 km. As previous studies show, in south-central Hokkaido, the Hidaka collision zone is formed, and anomalous deep and thickened forearc crust material is subducting at depths of less than 70 km. The mainshock and its aftershocks are located at depths of approximately 10 to 40 km within the lower crust of the anomalous deep and thickened curst near the uppermost mantle material intrusions in the northwestern edge of this Hidaka collision zone. Like the two previous large events, the aftershocks of this event incline steeply eastward and appear to be distributed in the deeper extension of the Ishikari-teichi-toen fault zone. The highly inclined fault in the present study is consistent with a fault model by a geodetic analysis with InSAR. The aftershocks at depths of 10 to 20 km are located at the western edge of the high-attenuation (low-Qp) zone. These kinds of relationships between hypocenters and materials are the same as the 1970 and 1982 events in the Hidaka collision zone. The anomalous large focal depths of these large events compared with the average depth limit of inland earthquakes in Japan could be caused by the locally lower temperature in south-central Hokkaido. This event is one of the approximately M7 large inland earthquakes that occurred repeatedly at a recurrence interval of approximately 40 years and is important in the collision process in the Hidaka collision zone.

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