scholarly journals Toward Using Seismic Interferometry to Quantify Landscape Mechanical Variations after Earthquakes

2021 ◽  
Author(s):  
Odin Marc ◽  
Christoph Sens-Schönfelder ◽  
Luc Illien ◽  
Patrick Meunier ◽  
Manuel Hobiger ◽  
...  
Keyword(s):  
Landslide Susceptibility ◽  
Seismic Velocity ◽  
Landslide Hazard ◽  
Seismic Velocities ◽  
Surface Strength ◽  
Near Surface ◽  
Single Station ◽  
Seismic Velocity Changes ◽  
Velocity Changes ◽  
Large Earthquakes

ABSTRACT In mountainous terrain, large earthquakes often cause widespread coseismic landsliding as well as hydrological and hydrogeological disturbances. A subsequent transient phase with high landslide rates has also been reported for several earthquakes. Separately, subsurface seismic velocities are frequently observed to drop coseismically and subsequently recover. Consistent with various laboratory work, we hypothesize that the seismic-velocity changes track coseismic damage and progressive recovery of landscape substrate, which modulate landslide hazard and hydrogeological processes, on timescales of months to years. To test this, we analyze the near-surface seismic-velocity variations, obtained with single-station high-frequency (0.5–4 Hz) passive image interferometry, in the epicentral zones of four shallow earthquakes, for which constraints on landslide susceptibility through time exist. In the case of the 1999 Chi-Chi earthquake, detailed landslide mapping allows us to accurately constrain an exponential recovery of landslide susceptibility with a relaxation timescale of about 1 yr, similar to the pattern of recovery of seismic velocities. The 2004 Niigata, 2008 Iwate, and 2015 Gorkha earthquakes have less-resolved constraints on landsliding, but, assuming an exponential recovery, we also find matching relaxation timescales, from ∼0.1 to ∼0.6  yr, for the landslide and seismic recoveries. These observations support our hypothesis and suggest that systematic monitoring of seismic velocities after large earthquakes may help constrain and manage the evolution of landslide hazard in epicentral areas. To achieve this goal, we end by discussing several ways to improve the link between seismic velocity and landscape mechanical properties, specifically by better constraining time-dependent near-surface strength and hydrogeological changes. Hillslopes displaying coseismic surface fissuring and displacement may be an important target for future geotechnical analysis and coupled to passive geophysical investigations.

scholarly journals Physics-Based Relationship for Pore Pressure and Vertical Stress Monitoring Using Seismic Velocity Variations

2021 ◽  
Vol 13 (14) ◽  
pp. 2684
Author(s):  
Eldert Fokker ◽  
Elmer Ruigrok ◽  
Rhys Hawkins ◽  
Jeannot Trampert
Keyword(s):  
Pore Pressure ◽  
Seismic Velocity ◽  
Pressure Head ◽  
Groundwater Table ◽  
Surface Velocity ◽  
Seismic Velocities ◽  
Stress Monitoring ◽  
Near Surface ◽  
Velocity Variations ◽  
Velocity Changes

Previous studies examining the relationship between the groundwater table and seismic velocities have been guided by empirical relationships only. Here, we develop a physics-based model relating fluctuations in groundwater table and pore pressure with seismic velocity variations through changes in effective stress. This model justifies the use of seismic velocity variations for monitoring of the pore pressure. Using a subset of the Groningen seismic network, near-surface velocity changes are estimated over a four-year period, using passive image interferometry. The same velocity changes are predicted by applying the newly derived theory to pressure-head recordings. It is demonstrated that the theory provides a close match of the observed seismic velocity changes.

Revealing seasonal crustal seismic velocity variations in Taiwan with single-station cross-component analysis 

2021 ◽  
Author(s):  
Kuan-Fu Feng ◽  
Hsin-Hua Huang ◽  
Ya-Ju Hsu ◽  
Yih-Min Wu
Keyword(s):  
Pore Pressure ◽  
Seasonal Variations ◽  
Seismic Velocity ◽  
Pressure Change ◽  
Temporal Variations ◽  
Air Pressure ◽  
Weather Data ◽  
Single Station ◽  
Seismic Velocity Changes ◽  
Velocity Changes

<p>Ambient noise interferometry is a promising technique for studying crustal behaviors, providing continuous measurements of seismic velocity changes (dv/v) in relation to physical processes in the crust over time. In addition to the tectonic-driven dv/v changes, dv/v is also known to be affected by environmental factors through rainfall-induced pore-pressure changes, air pressure loading changes, thermoelastic effects, and so forth. In this study, benefiting from the long-term continuous data of Broadband Array in Taiwan for Seismology (BATS) that has been operated since 1994, we analyze continuous seismic data from 1998 to 2019 by applying single-station cross-component (SC) technique to investigate the temporal variations of crust on seismic velocity. We process the continuous waveforms of BATS stations, construct the empirical Green’s functions, and compute daily seismic velocity changes by the stretching technique in a frequency band of 0.1 to 0.9 Hz. We observe co-seismic velocity drops associated with the inland moderate earthquakes. Furthermore, clear seasonal cycles, with a period of near one-year, are also revealed at most stations, but with different characteristics. Systematic spectral and time-series analyses with the weather data are conducted and show that the rainfall-induced pore-pressure change is likely the main cause to the seasonal variations with high correlations. The strong site-dependency of these seasonal variations also precludes air pressure and temperature which varies smoothly in space from being dominant sources and suggests spatially-varying complex hydro-mechanical interaction across the orogenic belt in Taiwan.</p>

Near-salt stress-induced seismic velocity changes and seismic anisotropy and their impacts on salt imaging: A case study in the Kuqa depression, Tarim Basin, China

2020 ◽  
Vol 8 (3) ◽  
pp. T487-T499
Author(s):  
Yunqiang Sun ◽  
Gang Luo ◽  
Yaxing Li ◽  
Mingwen Wang ◽  
Xiaofeng Jia ◽  
...  
Keyword(s):  
Salt Stress ◽  
Seismic Anisotropy ◽  
Velocity Structure ◽  
Seismic Velocity ◽  
Seismic Velocities ◽  
Kuqa Depression ◽  
Velocity Models ◽  
Salt Structure ◽  
Seismic Velocity Changes ◽  
Velocity Changes

It has been recognized that stress perturbations in sediments induced by salt bodies can cause elastic-wave velocity (seismic velocity) changes and seismic anisotropy through changing their elastic parameters, thus leading to difficulties in salt imaging. To investigate seismic velocity changes and seismic anisotropy by near-salt stress perturbations and their impacts on salt imaging, taking the Kuqa depression as an example, we have applied a 2D plane-strain static geomechanical finite-element model to simulate stress perturbations and calculate the associated seismic velocity changes and seismic anisotropy; then we used the reverse time migration and imaging method to image the salt structure by excluding and including the stress-induced seismic velocity changes. Our model results indicate that near-salt stresses are largely perturbed due to salt stress relaxation, and the stress perturbations lead to significant changes of the seismic velocities and seismic anisotropy near the salt structure: The maximum seismic velocity changes can reach approximately 20% and the maximum seismic anisotropy can reach approximately 10%. The significant changes of seismic velocities due to stress perturbations largely impact salt imaging: The salt imaging is unclear, distorted, or even failed if we exclude near-salt seismic velocity changes from the preliminary velocity structure, but the salt can be better imaged if the preliminary velocity structure is modified by near-salt seismic velocity changes. We find that the locations where salt imaging tends to fail usually occur where large seismic velocity changes happen, and these locations are clearly related to the geometric characteristics of salt bodies. To accurately image the salt, people need to integrate results of geomechanical models and stress-induced seismic velocity changes into the imaging approach. The results provide petroleum geologists with scientific insights into the link between near-salt stress perturbations and their induced seismic velocity changes and help exploration geophysicists build better seismic velocity models in salt basins and image salt accurately.

scholarly journals Crustal seismic velocity responds to a magmatic intrusion and seasonal loading in Iceland’s Northern Volcanic Zone

2019 ◽  
Vol 5 (11) ◽  
pp. eaax6642 ◽  
Author(s):  
C. Donaldson ◽  
T. Winder ◽  
C. Caudron ◽  
R. S. White
Keyword(s):  
Atmospheric Pressure ◽  
Seismic Velocity ◽  
Volumetric Strain ◽  
Volcanic Zone ◽  
Noise Interferometry ◽  
Crustal Stresses ◽  
Single Station ◽  
Seismic Velocity Changes ◽  
Velocity Changes ◽  
Snow Thickness

Seismic noise interferometry is an exciting technique for studying volcanoes, providing a continuous measurement of seismic velocity changes (dv/v), which are sensitive to magmatic processes that affect the surrounding crust. However, understanding the exact mechanisms causing changes in dv/v is often difficult. We present dv/v measurements over 10 years in central Iceland, measured using single-station cross-component correlation functions from 51 instruments across a range of frequency bands. We observe a linear correlation between changes in dv/v and volumetric strain at stations in regions of both compression and dilatation associated with the 2014 Bárðarbunga-Holuhraun dike intrusion. Furthermore, a clear seasonal cycle in dv/v is modeled as resulting from elastic and poroelastic responses to changing snow thickness, atmospheric pressure, and groundwater level. This study comprehensively explains variations in dv/v arising from diverse crustal stresses and highlights the importance of deformation modeling when interpreting dv/v, with implications for volcano and environmental monitoring worldwide.

Seismic velocity changes in the epicentral area of the Mw 7.8 Pedernales (Ecuador) earthquake from cross-correlation of ambient seismic noise

2020 ◽  
Author(s):  
Hans Agurto-Detzel ◽  
Diane Rivet ◽  
Philippe Charvis
Keyword(s):  
Seismic Noise ◽  
Cross Correlation ◽  
Seismic Velocity ◽  
Healing Process ◽  
Ambient Seismic Noise ◽  
Crustal Material ◽  
Seismic Velocities ◽  
Epicentral Area ◽  
Seismic Velocity Changes ◽  
Velocity Changes

<p>In the last decade, correlation of ambient seismic noise has opened a window to new possibilities for the study of structural properties of the Earth. One such possibility is the monitoring of transient changes in the mechanical properties of the surrounding crustal material following an earthquake. These changes, expressed as variations in seismic velocities, are usually associated to fracture damage and release of fluids due to the earthquakes shaking, but could also be related to deformation associated with afterslip. On April 16, 2016, a Mw 7.8 earthquake struck the coast of Ecuador, rupturing a ~100 km-long segment of the megathrust interface previously identified as highly coupled. Shortly after the mainshock, we deployed a temporary seismic network to monitor the post-seismic phase, in addition to the already in-place permanent Ecuadorian network. Here we present results from cross-correlation of continuous ambient seismic noise during a ~12-months period following the mainshock. Taking advantage of the dense and extensive station network, we investigate the spatio-temporal evolution of the post-seimic seismic velocity changes. Our results show a slow but sustained increase in the average seismic velocities after the earthquake, with a decay in the rate of the increase during the last few months. Spatially, the increase is more notorious nearby the rupture area, whereas the amplitude of the increase diminishes as we move away from the epicenter. We interpret these variations in seismic velocities (steady increase) as the crust’s response to the healing process that takes place during the post-seismic phase, following the sudden coseismic decrease of seismic velocities during the mainshock. This healing process could involve the decrease of fluid-related pore pressures and the healing of fractures and cracks generated during the mainshock, both at the interface and on the overriding plate.</p>

scholarly journals Seismic Velocity Response to Atmospheric Pressure Using Time-Lapse Passive Seismic Interferometry

2021 ◽  
Author(s):  
Chloé Gradon ◽  
Florent Brenguier ◽  
Johannes Stammeijer ◽  
Aurélien Mordret ◽  
Kees Hindriks ◽  
...  
Keyword(s):  
Atmospheric Pressure ◽  
Seismic Velocity ◽  
Barometric Pressure ◽  
Specific Response ◽  
Positive Trend ◽  
Seismic Velocities ◽  
Near Surface ◽  
Passive Seismic ◽  
Velocity Changes ◽  
Shallow Crust

ABSTRACT Seismic velocities in the shallow crust down to a few kilometers depth show a remarkable sensitivity to stress perturbations due to the presence of compliant pores, cracks, fractures, and faults. Monitoring temporal changes of seismic velocities can thus provide key insights on dynamic processes affecting the shallow crust such as those related to the atmosphere (rainfall, barometric pressure, and temperature) and those with deeper tectonic and volcanic origins. In this work, we investigate the specific response of the near surface down to 300 m depth to atmospheric pressure variations. We conduct a four month passive seismic monitoring experiment in the desert of Oman using continuous noise recorded at geophones located within five wells. The results show a clear, direct correlation between seismic velocities and barometric pressure variations for monthly transients. At a longer, seasonal temporal scale, seismic velocities are stable, whereas atmospheric pressure shows a clear positive trend. We use the undrained coupled poroelastic theory to model these observations and find that the lack of seasonal velocity changes can be partly explained by the atmospheric pressure that diffuses into the pores with a strong hydraulic diffusivity likely higher than 100  m2/s consistent with the local geology referring to carbonates. Finally, the comparison between the modeled and observed velocity changes leads to estimate a velocity–stress sensitivity on the order of 6.3×10−7  Pa−1 which is consistent with previous studies. Using this result for calibration, we find that a sudden step-change drop of velocity of 0.015% occurring in the beginning of October 2019 and corresponding to a stress perturbation likely larger than 240 Pa affected the entire studied area. This small change could be related to a perturbation at greater depth associated with variations in the production rates within the underlying reservoir.

Regional seismic velocity changes following the 2019 Mw7.1 Ridgecrest California earthquake from autocorrelations and P/S converted waves

2021 ◽  
Author(s):  
Y Lu ◽  
Y Ben-Zion
Keyword(s):  
Temporal Resolution ◽  
Seismic Velocity ◽  
Time Windows ◽  
Regional Scale ◽  
Early Period ◽  
Temporal Changes ◽  
High Temporal Resolution ◽  
Seismic Velocities ◽  
Seismic Velocity Changes ◽  
Velocity Changes

Summary We examine regional transient changes of seismic velocities generated by the Mw 7.1 2019 Ridgecrest earthquake in California, using autocorrelations of moving time windows in continuous waveforms recorded at regional stations. We focus on travel time differences in a prominent phase generated by an interface around 2 km depth, associated with transmitted Pp waves and converted Ps waves from the ongoing microseismicity. Synthetic tests demonstrate the feasibility of the method for monitoring seismic velocity changes. Taking advantage of the numerous aftershocks in the early period following the mainshock, we obtain a temporal resolution of velocity changes up to 20 min in the early post-mainshock period. The results reveal regional coseismic velocity drops in the top 1–3 km with an average value of ∼2 per cent over distances up to 100 km from the Ridgecrest event. These average velocity drops are likely dominated by larger changes in the shallow materials, and are followed by rapid recoveries on timescales of days. Around the north end of the Ridgecrest rupture and the nearby Coso geothermal region, the observed coseismic velocity drops are up to ∼8 per cent. The method allows monitoring temporal changes of seismic velocities with high temporal resolution, fast computation, and precise spatial mapping of changes. The results suggest that significant temporal changes of seismic velocities of shallow materials are commonly generated on a regional scale by large events.

Single-station seismic monitoring of permafrost on Mt. Zugspitze (Germany) over the past 15 years

2021 ◽  
Author(s):  
Fabian Lindner ◽  
Joachim Wassermann
Keyword(s):  
Travel Time ◽  
Seismic Velocity ◽  
Temperature Record ◽  
Lapse Time ◽  
Resistivity Tomography ◽  
Single Station ◽  
Velocity Variations ◽  
Spatio Temporal ◽  
Velocity Changes ◽  
Permafrost Thawing

<p>Permafrost thawing affects mountain slope stability and can trigger hazardous rock falls. As rising temperatures promote permafrost thawing, spatio-temporal monitoring of long-term and seasonal variations in the perennially frozen rock is therefore crucial in regions with high hazard potential. With various infrastructure in the summit area and population in the close vicinity, Mt. Zugspitze in the German/Austrian Alps is such a site and permafrost has been monitored with temperature logging in boreholes and lapse-time electrical resistivity tomography. Yet, these methods are expensive and laborious, and are limited in their spatial and/or temporal resolution.</p><p>Here, we analyze continuous seismic data from a single station deployed at an altitude of 2700 m a.s.l. in a research station, which is separated by roughly 250 m from the permafrost affected ridge of Mt. Zugspitze. Data are available since 2006 (with some gaps) and reveal high-frequency (>1 Hz) anthropogenic noise likely generated by the cable car stations at the summit. We calculate single-station cross-correlations between the different sensor components and investigate temporal coda wave changes by applying the recently introduced wavelet-based cross-spectrum method. This approach provides time series of the travel time relative to the reference stack as a function of frequency and lag time in the correlation functions. In the frequency and lag range of 1-10 Hz and 0.5-5 s respectively, we find various parts in the coda that show clear annual variations and an increasing trend in travel time over the past 15 years of consideration. Converting the travel time variations to seismic velocity variations (assuming homogeneous velocity changes affecting the whole mountain) results in seasonal velocity changes of up to a few percent and on the order of 0.1% decrease per year. Yet, estimated velocity variations do not scale linearly with lag time, which indicates that the medium changes are localized rather than uniform and that the absolute numbers need to be taken with caution. The annual velocity variations are anti-correlated with the temperature record from the summit but delayed by roughly one month.</p><p>The phasing of the annual seismic velocity change (relative to the temperature record) is in agreement with a previous study employing lapse-time electrical resistivity tomography. Furthermore, the decreasing trend in seismic velocity happens concurrently with an increasing trend in temperature. The results therefore suggest that the velocity changes are related to seasonal thaw and refreeze and permafrost degradation and thus highlight the potential of seismology for permafrost monitoring. By adding additional receivers and/or a fiber-optic cable for distributed acoustic sensing, hence increasing the spatial resolution, the presented method holds promise for lapse-time imaging of permafrost bodies with high spatio-temporal resolution from passive measurements.</p>

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