Scattering strength at active volcanoes in Japan as inferred from the peak ratio analysis of teleseismic P waves

AbstractSmall-scale seismic velocity heterogeneity has been studied through the calculation of peak amplitude ratio as a means to quantify the strength of seismic wave scattering at volcanoes in Japan. This ratio is defined as the ratio of the maximum (peak) P wave energy in the transverse component seismogram envelope over that of the three-component sum seismogram envelope (transverse + radial + vertical). According to the previous study using Japan’s Hi-net seismometer network, the peak ratio is observed to be larger near the (active) quaternary volcanoes. However, these Hi-net stations are not positioned on the volcanoes themselves. This study systematically examines the peak ratios at 47 active volcanoes across Japan, using seismometers operated by the Japan Meteorological Agency (JMA). Analyses were performed at four frequency bands: 0.5–1, 1–2, 2–4, and 4–8 Hz. We found that the JMA stations yield higher peak ratios than the Hi-net stations. Their differences are statistically significant at the 99.9% confidence level in all frequency bands. We also examined the differences between the ground surface and borehole stations of the JMA network. The former shows larger peak ratios, and for most frequency bands, the differences are also statistically significant at the 99.9% confidence level. This suggests an intensification of small-scale medium heterogeneities especially at shallow depths at active volcanoes, and that scattering might have been enhanced at the very shallow parts. Graphical Abstract

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Different mechanisms of the pre- and co-eruptive tremor during the 2018 eruption at Sierra Negra volcano, Galapagos

10.5194/egusphere-egu2020-18975 ◽

2020 ◽

Author(s):

Ka Lok Li ◽

Meysam Rezaeifar ◽

Christopher J. Bean ◽

James Grannell ◽

Andrew Bell ◽

...

Keyword(s):

Frequency Band ◽

Velocity Structure ◽

Amplitude Ratio ◽

Volcanic Tremor ◽

Time Lapse ◽

P Wave ◽

Ratio Method ◽

Sierra Negra Volcano ◽

Sierra Negra ◽

Active Volcanoes

Volcanic tremor are persistent seismic signals observed near active volcanoes. They are often associated with eruptions, although the exact relationships are not well constrained. To gain a better insight into the generation mechanisms of volcanic tremor, we study tremor that occurred during the 2018 eruption at Sierra Negra volcano, Galapagos. Located 1000 km west of continental Ecuador, Sierra Negra is a shield volcano with a large summit caldera and is one of the most active volcanoes in the Galapagos archipelago. The 2018 eruption started at about 19:55 UTC on 26th June and lasted about two months. Two tremor phases with very different frequency characteristics are identified before and after the eruption onset. The pre-eruptive phase is characterized by a narrow frequency band (2.5 &#8211; 4 Hz) and the co-eruptive phase has a broad frequency band (1 &#8211; 15 Hz). Location of the two phases by a seismic amplitude ratio method suggests that they are likely to be generated by different physical processes. The pre-eruptive phase is likely generated by dike opening while the co-eruptive phase is associated with lava flow. This interpretation is consistent with a time-lapse P-wave velocity structure of the volcano imaged by local-earthquake travel-time tomography.

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

Journal of Environmental and Engineering Geophysics ◽

10.32389/jeeg9-067 ◽

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.

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

Geophysical Journal International ◽

10.1093/gji/ggab037 ◽

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.

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Seismic tomographic interpretation of Paleozoic sedimentary sequences in the southeastern North Sea

Geophysics ◽

10.1190/1.1996908 ◽

2005 ◽

Vol 70 (4) ◽

pp. R45-R56 ◽

Cited By ~ 10

Author(s):

Lars Nielsen ◽

Hans Thybo ◽

Martin Glendrup

Keyword(s):

North Sea ◽

Velocity Structure ◽

Seismic Velocity ◽

P Wave ◽

Wide Angle ◽

North German Basin ◽

Sedimentary Sequences ◽

The North ◽

Crystalline Crust ◽

German Basin

Seismic wide-angle data were recorded to more than 300-km offset from powerful airgun sources during the MONA LISA experiments in 1993 and 1995 to determine the seismic-velocity structure of the crust and uppermost mantle along three lines in the southeastern North Sea with a total length of 850 km. We use the first arrivals observed out to an offset of 90 km to obtain high-resolution models of the velocity structure of the sedimentary layers and the upper part of the crystalline crust. Seismic tomographic traveltime inversion reveals 2–8-km-thick Paleozoic sedimentary sequences with P-wave velocities of 4.5–5.2 km/s. These sedimentary rocks are situated below a Mesozoic-Cenozoic sequence with variable thickness: ∼2–3 km on the basement highs, ∼2–4 km in the Horn Graben and the North German Basin, and ∼6–7 km in the Central Graben. The thicknesses of the Paleozoic sedimentary sequences are ∼3–5 km in the Central Graben, more than 4 km in the Horn Graben, up to ∼4 km on the basement highs, and up to 8 km in the North German Basin. The Paleozoic strata are clearly separated from the shallower and younger sequences with velocities of ∼1.8–3.8 km/s and the deeper crystalline crust with velocities of more than 5.8–6.0 km/s in the tomographic P-wave velocity model. Resolution tests show that the existence of the Paleozoic sediments is well constrained by the data. Hence, our wide-angle seismic models document the presence of Paleozoic sediments throughout the southeastern North Sea, both in the graben structures and in deep basins on the basement highs.

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Reliability Assessment of Tunnel Based on P -Wave Seismic Velocity

International Journal of Geomechanics ◽

10.1061/(asce)gm.1943-5622.0001245 ◽

2018 ◽

Vol 18 (11) ◽

pp. 06018030

Author(s):

Xiao-Ping Zhou ◽

Xiao-Cheng Huang ◽

Jin-Xin Li

Keyword(s):

Seismic Velocity ◽

Reliability Assessment ◽

P Wave

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Near-surface glaciotectonic structures in the sediments of an overdeepened glacial valley revealed by a shallow 3D seismic survey

10.5194/egusphere-egu21-8195 ◽

2021 ◽

Author(s):

David Tanner ◽

Hermann Buness ◽

Thomas Burschil

Keyword(s):

Seismic Reflection ◽

P Wave ◽

Seismic Survey ◽

Small Scale ◽

Academic Press ◽

Near Surface ◽

Glacial Sediments ◽

Area Source ◽

Terminal Moraine ◽

Rhine Valley

Glaciotectonic structures commonly include thrusting and folding, often as multiphase deformation. Here we present the results of a small-scale 3-D P-wave seismic reflection survey of glacial sediments within an overdeepened glacial valley in which we recognise unusual folding structures in front of push-moraine. The study area is in the Tannwald Basin, in southern Germany, about 50 km north of Lake Constance, where the basin is part of the glacial overdeepened Rhine Valley. The basin was excavated out of Tertiary Molasse sediments during the Hosskirchian stage, and infilled by 200 m of Hosskirchian and Rissian glacioclastics (Dietmanns Fm.). After an unconformity in the Rissian, a ca. 7 m-thick till (matrix-supported diamicton) was deposited, followed by up to 30 m of Rissian/W&#252;rmian coarse gravels and minor diamictons (Illmensee Fm.). The terminal moraine of the last W&#252;rmian glaciation overlies these deposits to the SW, not 200 m away.We conducted a 3-D, 120 x 120 m&#178;, P-wave seismic reflection survey around a prospective borehole site in the study area. Source/receiver points and lines were spaced at 3 m and 9 m, respectively. A 10 s sweep of 20-200 Hz was excited by a small electrodynamic, wheelbarrow-borne vibrator twice at every of the 1004 realized shot positions. We recognised that the top layer of coarse gravel above the till is folded, but not in the conventional buckling sense, rather as cuspate-lobate folding. The fold axes are parallel to the terminal moraine front. The wavelength of the folding varies between 40 and 80 m, and the thickness of the folded layer is on average about 20 m. Cuspate-lobate folding is typical for deformation of layers of differing mechanical competence (after Ramsay and Huber 1987; &#181;1/&#181;2 less than 10), so this tell us something about the relative competence (or stiffness) of the till layer compared to the coarse clastics above. We also detected small thrust faults that are also parallel to the push-moraine, but these have very little offset and most of the deformation was achieved by folding.Ramsay, J.G. and Huber, M. I. (1987): The techniques of modern structural geology, vol. 2: Folds and fractures: Academic Press, London, 700 pp.

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Noise-based ballistic wave passive seismic monitoring. Part 1: body waves

Geophysical Journal International ◽

10.1093/gji/ggz440 ◽

2020 ◽

Vol 221 (1) ◽

pp. 683-691 ◽

Cited By ~ 5

Author(s):

F Brenguier ◽

R Courbis ◽

A Mordret ◽

X Campman ◽

P Boué ◽

...

Keyword(s):

Seismic Velocity ◽

Noise Source ◽

Seismic Monitoring ◽

Body Waves ◽

P Wave ◽

New Technique ◽

Apparent Velocity ◽

Near Surface ◽

Velocity Increase ◽

Passive Seismic

SUMMARY Unveiling the mechanisms of earthquake and volcanic eruption preparation requires improving our ability to monitor the rock mass response to transient stress perturbations at depth. The standard passive monitoring seismic interferometry technique based on coda waves is robust but recovering accurate and properly localized P- and S-wave velocity temporal anomalies at depth is intrinsically limited by the complexity of scattered, diffracted waves. In order to mitigate this limitation, we propose a complementary, novel, passive seismic monitoring approach based on detecting weak temporal changes of velocities of ballistic waves recovered from seismic noise correlations. This new technique requires dense arrays of seismic sensors in order to circumvent the bias linked to the intrinsic high sensitivity of ballistic waves recovered from noise correlations to changes in the noise source properties. In this work we use a dense network of 417 seismometers in the Groningen area of the Netherlands, one of Europe's largest gas fields. Over the course of 1 month our results show a 1.5 per cent apparent velocity increase of the P wave refracted at the basement of the 700-m-thick sedimentary cover. We interpret this unexpected high value of velocity increase for the refracted wave as being induced by a loading effect associated with rainfall activity and possibly canal drainage at surface. We also observe a 0.25 per cent velocity decrease for the direct P-wave travelling in the near-surface sediments and conclude that it might be partially biased by changes in time in the noise source properties even though it appears to be consistent with complementary results based on ballistic surface waves presented in a companion paper and interpreted as a pore pressure diffusion effect following a strong rainfall episode. The perspective of applying this new technique to detect continuous localized variations of seismic velocity perturbations at a few kilometres depth paves the way for improved in situ earthquake, volcano and producing reservoir monitoring.

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Density-Depth Profile Determined by Seismic-Refraction Studies: Ice Stream B. West Antarctica (Abstract)

Annals of Glaciology ◽

10.1017/s0260305500006546 ◽

1988 ◽

Vol 11 ◽

pp. 198 ◽

Cited By ~ 3

Author(s):

S. Anandakrishnan

Keyword(s):

Shear Wave ◽

Seismic Velocity ◽

Austral Summer ◽

P Wave ◽

S Wave ◽

Data Logger ◽

High Resolution Data ◽

Ice Stream ◽

Wave Profiles ◽

Depth Curve

Detailed seismic short-refraction profiling was conducted on Ice Stream Β (UpB) during the 1983–84 austral summer. A new high-resolution data logger, developed at the University of Wisconsin, recorded both compressional- and shear-wave arrivals. We report here on P-wave and S-wave profiles recorded along a line parallel to the axis of the ice stream. Source-receiver separations up to 720 m yielded seismic velocity-depth curves to below the firn-ice transition zone (slightly greater than 30 m at UpB). For the compressional-wave profile, geophones were separated by 2.5 m, which yielded a velocity-depth curve with a granularity of ∼1 m. The corresponding density-depth curve agrees well with direct density measurements obtained from a core extracted nearby (Alley and Bentley 1988, this volume). Discontinuities in the velocity gradient do not appear at the “critical densities” as they did at Byrd Station, Antarctica, and elsewhere (Kohnen and Bentley 1973 , Robertson and Bentley 1975). Two shear-wave profiles were recorded, both with geophone spacings of 5 m, one with longitudinal polarization (SV) and the other with transverse polarization (SH). There is a marked difference in velocity between the SH and SV waves, particularly in the shallow firn. We suggest that a strong vertical shape-and-bonding fabric in the shallow firn, as observed in cores collected at UpB, would account for this disparity.

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The 1998 Valhall microseismic data set: An integrated study of relocated sources, seismic multiplets, and S-wave splitting

Geophysics ◽

10.1190/1.3205028 ◽

2009 ◽

Vol 74 (5) ◽

pp. B183-B195 ◽

Cited By ~ 40

Author(s):

K. De Meersman ◽

J.-M. Kendall ◽

M. van der Baan

Keyword(s):

Seismic Anisotropy ◽

Amplitude Ratio ◽

Temporal Variations ◽

Oil Field ◽

P Wave ◽

Wave Form ◽

S Wave ◽

Data Set ◽

Wave Splitting ◽

Source Mechanisms

We relocate 303 microseismic events recorded in 1998 by sensors in a single borehole in the North Sea Valhall oil field. A semiautomated array analysis method repicks the P- and S-wave arrival times and P-wave polarizations, which are needed to locate these events. The relocated sources are confined predominantly to a [Formula: see text]-thick zone just above the reservoir, and location uncertainties are half those of previous efforts. Multiplet analysis identifies 40 multiplet groups, which include 208 of the 303 events. The largest group contains 24 events, and five groups contain 10 or more events. Within each multiplet group, we further improve arrival-time picking through crosscorrelation, which enhances the relative accuracy of the relocated events and reveals that more than 99% of the seismic activity lies spatially in three distinct clusters. The spatial distribution of events and wave-form similarities reveal two faultlike structures that match well with north-northwest–south-southeast-trending fault planes interpreted from 3D surface seismic data. Most waveform differences between multiplet groups located on these faults can be attributed to S-wave phase content and polarity or P-to-S amplitude ratio. The range in P-to-S amplitude ratios observed on the faults is explained best in terms of varying source mechanisms. We also find a correlation between multiplet groups and temporal variations in seismic anisotropy, as revealed by S-wave splitting analysis. We explain these findings in the context of a cyclic recharge and dissipation of cap-rock stresses in response to production-driven compaction of the underlying oil reservoir. The cyclic nature of this mechanism drives the short-term variations in seismic anisotropy and the reactivation of microseismic source mechanisms over time.

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Effect of centimetric freezing of the near subsurface on Rayleigh and Love wave velocity in ambient seismic noise correlations

Geophysical Journal International ◽

10.1093/gji/ggaa406 ◽

2020 ◽

Vol 224 (1) ◽

pp. 626-636

Author(s):

René Steinmann ◽

Céline Hadziioannou ◽

Eric Larose

Keyword(s):

Surface Wave ◽

Wave Velocity ◽

Love Wave ◽

Ambient Noise ◽

Seismic Velocity ◽

Environmental Parameters ◽

Velocity Variation ◽

Small Scale ◽

Apparent Velocity ◽

Velocity Variations

SUMMARY About a decade ago, noise-based monitoring became a key tool in seismology. One of the tools is passive image interferometry (PII), which uses noise correlation functions (NCF) to retrieve seismic velocity variations. Most studies apply PII to vertical components recording oceanic low-frequent ambient noise ( < 1 Hz). In this work, PII is applied to high-frequent urban ambient noise ( > 1 Hz) on three three-component sensors. With environmental sensors inside the subsurface and in the air, we are able to connect observed velocity variations with environmental parameters. Temperatures below 0 °C correlate well with strong shear wave velocity increases. The temperature sensors inside the ground suggest that a frozen layer of less than 5 cm thickness causes apparent velocity increases above 2 % , depending on the channel pair. The observations indicate that the different velocity variation retrieved from the different channel pairs are due to different surface wave responses inherent in the channel pairs. With dispersion curve modelling in a 1-D medium we can verify that surfaces waves of several tens of metres wavelength experience a velocity increase of several percent due to a centimetres thick frozen layer. Moreover, the model verifies that Love waves show larger velocity increases than Rayleigh waves. The findings of this study provide new insights for monitoring with PII. A few days with temperature below 0 °C can already mask other potential targets (e.g. faults or storage sites). Here, we suggest to use vertical components, which is less sensitive to the frozen layer at the surface. If the target is the seasonal freezing, like in permafrost studies, we suggest to use three-component sensors in order to retrieve the Love wave response. This opens the possibility to study other small-scale processes at the shallow subsurface with surface wave responses.

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