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  • ddc:551.22  (8)
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  • 2020-2023  (8)
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  • 1
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    Slow Slip Triggers the 2018 Mw 6.9 Zakynthos Earthquake Within the Weakly Locked Hellenic Subduction System, Greece (2021)
    Details
    Publikationsdatum: 2022-03-25
    Beschreibung: Slow slip events (SSEs) at subduction zones can precede large‐magnitude earthquakes and may serve as precursor indicators, but the triggering of earthquakes by slow slip remains insufficiently understood. Here, we combine geodetic, Coulomb wedge and Coulomb failure‐stress models with seismological data to explore the potential causal relationship between two SSEs and the 2018 Mw 6.9 Zakynthos Earthquake within the Hellenic Subduction System. We show that both SSEs released up to 10 mm of aseismic slip on the plate‐interface and were accompanied by an increase in upper‐plate seismicity rate. While the first SSE in late 2014 generated only mild Coulomb failure stress changes (≤3 kPa), that were nevertheless sufficient to destabilize faults of various kinematics in the overriding plate, the second SSE in 2018 caused stress changes up to 25 kPa prior to the mainshock. Collectively, these stress changes affected a highly overpressured and mechanically weak forearc, whose state of stress fluctuated between horizontal deviatoric compression and tension during the years preceding the Zakynthos Earthquake. We conclude that this configuration facilitated episodes of aseismic and seismic deformation that ultimately triggered the Zakynthos Earthquake.
    Beschreibung: Key Points: Two slow‐slip events (each ≤10 mm) on the plate‐interface of the western Hellenic subduction system are explored. Stress perturbations due to slow‐slip promoted failure of upper‐plate faults and triggered the 2018 Mw 6.9 Zakynthos Earthquake. The forearc is mechanically weak and small friction changes on the megathrust with time, may reverse the stress‐state in the upper‐plate.
    Schlagwort(e): ddc:551.22
    Sprache: Englisch
    Materialart: doc-type:article
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  • 2
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    Age Uncertainty in Recurrence Analysis of Paleoseismic Records (2021)
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    Publikationsdatum: 2022-03-24
    Beschreibung: Determining the aperiodicity of large earthquake recurrences is key to forecast future rupture behavior. Aperiodicity is classically expressed as the coefficient of variation of recurrence intervals, though the recent trend to express it as burstiness is more intuitive and avoids minor inaccuracies. Due to the underestimation of burstiness in records with a low number of recurrence intervals, the paradigm is to obtain long paleoseismic records with many events. Here, we present a suite of synthetic paleoseismic records designed around the Weibull and inverse Gaussian distributions that demonstrate that age uncertainty relative to the mean recurrence interval causes overestimation of burstiness. The effects of overestimation and underestimation interact and give complex results for accurate estimates of aperiodicity. Furthermore, we show that the way recurrence intervals are sampled from a paleoseismic record can have strong influences on the resulting statistic and its implication for probabilistic seismic hazard assessment. Comparing values of burstiness between paleoseismic records should therefore be done with caution.
    Beschreibung: Plain Language Summary: To forecast future earthquake activity, paleoseismologists aim to have many events in a single sedimentary record to estimate the periodicity of an earthquake sequence with as little uncertainty as possible. This focus on the number of events is not wrong, but event age uncertainty is another—often neglected and not yet described—source of uncertainty that can interfere in estimating periodicity correctly. In this study, we show in what way and by how much event age uncertainty affects the uncertainty in periodicity. We create a model of many different artificial earthquake sequences. For our model setup, we choose: (1) two types of patterns; (2) six degrees of periodicity; (3) 10 different levels of event age uncertainty; and (4) a wide range of number of events (from 4 to 101 events). Then we create 50,000 earthquake sequences for each unique combination within this spectrum and analyze the variability in periodicity. We find that low number of events underestimates periodicity and high age uncertainty overestimates periodicity. Having many events in a record is more important, if the earthquake sequence is not periodic. Having accurately dated events is more important, if the earthquake sequence is periodic.
    Beschreibung: Key Points: Low number of recurrence intervals in paleoseismic records underestimates aperiodicity. High age uncertainty relative to the mean recurrence interval in paleoseismic records overestimates aperiodicity. For calculating coefficient of variation and burstiness it matters how recurrence intervals are sampled from records.
    Beschreibung: Deutsche Forschungsgemeinschaft (DFG) http://dx.doi.org/10.13039/501100001659
    Schlagwort(e): ddc:551.22
    Sprache: Englisch
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  • 3
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    Spatio‐Temporal Evolution of Earthquake Static Stress Drop Values in the 2016–2017 Central Italy Seismic Sequence (2021)
    Details
    Publikationsdatum: 2022-03-29
    Beschreibung: The static stress drop of an earthquake is an indicator of the stress state of a specific fault before rupture initiation. The stress state is primarily controlled by the ambient stress field, fault strength, fault complexity, and the presence of fluids. This study aims to investigate the spatio‐temporal distribution of static stress drop values of the 2016–2017 multi‐fault rupture seismic sequence in central Italy, which includes three earthquakes with Mw ≥ 5.9 (Amatrice, Visso, and Norcia earthquakes), and over 95,000 aftershocks (M 0.5–6.5). We estimate stress drop values using a circular crack model with corner frequency and seismic moment estimates from single‐spectra fitting, a cluster‐event method, and spectral‐ratio fitting. The temporal distribution of stress drop values shows an apparent increase of stress drop following a large earthquake (Mw ≥ 5.9). The spatial distribution shows comparably high stress drop values for early aftershocks surrounding the mainshock rupture area. High stress drop events correlate with fault complexity, such as fault intersections at depth and reactivated thrust fronts. We observe a constant stress drop for Mw ≥ ∼3, in contrast to previous studies. Instrument response and signal‐to‐noise bandwidth limitations likely govern the observed decrease in stress drop with decreasing magnitude for events with Mw ≤ 3. The spatio‐temporal distribution of stress drop values in a complex seismic sequence could support a more complete understanding of the earthquake rupture process and the evolution of seismic sequences. It could also highlight areas where stress loading is focused, which would have implications for short and intermediate term seismic hazard estimates.
    Beschreibung: Plain Language Summary: The ongoing earthquake sequence that began in 2016 in central Italy has produced a significant physical imprint on the earth's surface from the rupture of the three largest events, and has changed the state of stress within the crust. The earthquakes release stored stress in some regions, which can be measured indirectly by the waveforms recorded on seismometers (seismograms), and increase stress in others. Here we analyze seismograms, including those of numerous small earthquakes, to estimate source properties such as the physical size of the rupture surface and the corresponding fault slip. Source properties relate to the amount of stress released by an earthquake and are relevant to learning about the fault rupture process and the redistribution of stress during the evolution of a seismic sequence. We use a combination of approaches to find that the occurrence of large earthquakes leads to a temporal increase of stress in the vicinity of the ruptured fault, and that high stress release correlates with places where faults intersect in the subsurface. Our findings provide a more comprehensive picture of the complex seismic sequence and highlight areas that could influence short and intermediate term seismic hazard estimates.
    Beschreibung: Key Points: The AVN seismic sequence shows significant spatio‐temporal variations in stress drop values. Higher stress drop values correlate with increasing fault complexity and stress field heterogeneity. Instrument response and signal‐to‐noise limitations likely govern stress drop scaling for events with for M 〈 ∼3.
    Beschreibung: Deutsche Forschungsgemeinschaft (DFG) http://dx.doi.org/10.13039/501100001659
    Schlagwort(e): ddc:551.22
    Sprache: Englisch
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  • 4
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    Direct Evidence of a Slow‐Slip Transient Modulating the Spatiotemporal and Frequency‐Magnitude Earthquake Distribution: Insights From the Armutlu Peninsula, Northwestern Turkey (2022)
    Bocchini, G. M. ; Martínez‐Garzón, P. ; Verdecchia, A. ; [weitere]
    Details
    Publikationsdatum: 2022-12-05
    Beschreibung: Earthquakes and slow‐slip events interact, however, detailed studies investigating their interplay are still limited. We generate the highest resolution microseismicity catalog to date for the northern Armutlu Peninsula in a ∼1‐year period to perform a detailed seismicity distribution analysis and correlate the results with a local, geodetically observed slow‐slip transient within the same period. Seismicity shows a transition of cluster‐type behavior from swarm‐like to burst‐like, accompanied by an increasing relative proportion of clustered (non‐Poissonian) relative to background (Poissonian) seismicity and gradually decreasing b‐value as the geodetically observed slow‐slip transient ends. The observed slow‐slip transient decay correlates with gradually increasing effective‐stress‐drop values. The observed correlation between the b‐value and geodetic transient highlights the influence of aseismic deformation on seismic deformation and the impact of slow‐slip transients on local seismic hazard.
    Beschreibung: Plain Language Summary: Seismic and aseismic slip on faults can change the stress state in the crust and affect the recurrence time of earthquakes. Observations of how earthquakes and aseismic fault slip influence each other are limited because of the dearth of synchronous high‐resolution seismological and geodetic data. Here we use high‐resolution earthquake data in the northern Armutlu Peninsula along the Marmara seismic gap of the North Anatolian Fault (Turkey) to correlate the earthquake distribution with a local slow‐slip transient that occurred in the same period. We find that the slow‐slip transient modulates the spatiotemporal and frequency‐magnitude evolution of earthquakes, which highlights the influence of slow fault creep on fast fault slip. Our study demonstrates the importance of considering slow‐slip transients for seismic hazard assessment.
    Beschreibung: Key Points: Seismicity analysis suggests that both external and internal forcing drive deformation in the Armutlu Peninsula. Temporal correlation between a slow‐slip transient and seismic b‐value highlights interactions between aseismic and seismic deformation. Slow‐slip transients modulate the frequency‐magnitude and spatiotemporal earthquake distribution.
    Beschreibung: VW momentum grant
    Beschreibung: Helmotz Association Young Investigator Group http://dx.doi.org/10.13039/501100009318
    Beschreibung: Helmholtz‐Zentrum Potsdam—Deutsches GeoForschungs Zentrum GFZ, GIPP http://dx.doi.org/10.13039/501100010956
    Schlagwort(e): ddc:551.22 ; microseismicity ; enhanced catalog ; near‐fault monitoring ; seismic‐aseismic deformation ; slow‐slip transient
    Sprache: Englisch
    Materialart: doc-type:article
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  • 5
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    Limited Earthquake Interaction During a Geothermal Hydraulic Stimulation in Helsinki, Finland (2022)
    Kwiatek, Grzegorz ; Martínez‐Garzón, Patricia ; Davidsen, Jörn ; [weitere]
    Details
    Publikationsdatum: 2022-11-26
    Beschreibung: We investigate induced seismicity associated with a hydraulic stimulation campaign performed in 2020 in the 5.8 km deep geothermal OTN‐2 well near Helsinki, Finland as part of the St1 Deep Heat project. A total of 2,875 m3 of fresh water was injected during 16 days at well‐head pressures 〈70 MPa and with flow rates between 400 and 1,000 L/min. The seismicity was monitored using a high‐resolution seismic network composed of 10 borehole geophones surrounding the project site and a borehole array of 10 geophones located in adjacent OTN‐3 well. A total of 6,121 induced earthquakes with local magnitudes MLHel〉−1.9 ${M}_{\mathrm{L}}^{\mathrm{H}\mathrm{e}\mathrm{l}} 〉 -1.9$ were recorded during and after the stimulation campaign. The analyzed statistical parameters include magnitude‐frequency b‐value, interevent time and interevent time ratio, as well as magnitude correlations. We find that the b‐value remained stationary for the entire injection period suggesting limited stress build‐up or limited fracture network coalescence in the reservoir. The seismicity during the stimulation neither shows signatures of magnitude correlations, nor temporal clustering or anticlustering beyond those arising from varying injection rates. The interevent time statistics are characterized by a Poissonian time‐varying distribution. The calculated parameters indicate no earthquake interaction. Focal mechanisms suggest that the injection activated a spatially distributed network of similarly oriented fractures. The seismicity displays stable behavior with no signatures pointing toward a runaway event. The cumulative seismic moment is proportional to the cumulative hydraulic energy and the maximum magnitude is controlled by injection rate. The performed study provides a base for implementation of time‐dependent probabilistic seismic hazard assessment for the project site.
    Beschreibung: Plain Language Summary: We investigate anthropogenic seismicity associated with fluid injection into the 5.8 km deep geothermal OTN‐2 well near Helsinki, Finland, as a part of St1 Deep Heat Project. A total of 2,875 m3 of fresh water was injected during 16 days at well‐head pressures 〈70 MPa and with flow rates between 400 and 1,000 L/min. The seismicity was monitored using a seismic network composed of 20 borehole geophones located in Helsinki area and in the OTN‐3 well located close by the injection site. A total of 6,121 earthquakes indicating fractures of 1–30 m size were recorded during and after stimulation campaign. Using a handful of statistical properties derived from earthquake catalog we found no indication for earthquakes being triggered by other earthquakes. Instead, the earthquake activity rates, as well as the maximum earthquake size stayed proportional to the fluid injection rate. The spatio‐temporal behavior of seismicity and its properties suggest earthquakes occurred not on a single fault, but in a distributed network of similarly oriented fractures, limiting the possibility for occurrence of violent earthquakes. The performed study provides evidence that the induced seismicity due to injection performed within St1 Deep Heat project is stable and allow to constrain seismic hazard.
    Beschreibung: Key Points: Induced seismicity associated with stimulation campaign in a 5.8 km deep geothermal OTN‐2 well passively responds to injection operations. Seismicity is a non‐stationary Poisson process with seismicity rate and maximum magnitude modulated by the hydraulic energy input rate. Seismicity clusters in space and time in response to fluid injection but no interaction between earthquakes is observed.
    Beschreibung: Helmholtz Association http://dx.doi.org/10.13039/501100009318
    Beschreibung: https://doi.org/10.5880/GFZ.4.2.2022.001
    Schlagwort(e): ddc:551.22 ; induced seismicity ; hydraulic stimulation ; earthquake clustering ; earthquake interactions ; Poissonian distribution ; magnitude correlations ; interevent times
    Sprache: Englisch
    Materialart: doc-type:article
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  • 6
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    Rupture Heterogeneity and Directivity Effects in Back‐Projection Analysis (2022)
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    Publikationsdatum: 2022-06-21
    Beschreibung: The back projection method is a tremendously powerful technique for investigating the time dependent earthquake source, but its physical interpretation is elusive. We investigate how earthquake rupture heterogeneity and directivity can affect back‐projection results (imaged location and beam power) using synthetic earthquake models. Rather than attempting to model the dynamics of any specific real earthquake, we use idealized kinematic rupture models, with constant or varying rupture velocity, peak slip rate, and fault‐local strike orientation along unilateral or bilateral rupturing faults, and perform back‐projection with the resultant synthetic seismograms. Our experiments show back‐projection can track only heterogeneous rupture processes; homogeneous rupture is not resolved in our synthetic experiments. The amplitude of beam power does not necessarily correlate with the amplitude of any specific rupture parameter (e.g., slip rate or rupture velocity) at the back‐projected location. Rather, it depends on the spatial heterogeneity around the back‐projected rupture front, and is affected by the rupture directivity. A shorter characteristic wavelength of the source heterogeneity or rupture directivity toward the array results in strong beam power in higher frequency. We derive an equation based on Doppler theory to relate the wavelength of heterogeneity with synthetic seismogram frequency. This theoretical relation can explain the frequency‐ and array‐dependent back‐projection results not only in our synthetic experiments but also to analyze the 2019 M7.6 bilaterally rupturing New Ireland earthquake. Our study provides a novel perspective to physically interpret back‐projection results and to retrieve information about earthquake rupture characteristics.
    Beschreibung: Plain Language Summary: With the deployment of continental scale seismic arrays, seismologists can quickly locate the high‐frequency seismic radiation sources and track the earthquake rupture propagation using a technique called back‐projection. It is a signal beamforming technique application in seismology, and similar applications can be found in fields such as radar, wireless communication, and radio astronomy. Recent studies have proposed multiple advancements in improving the back‐projection location. However, the physical interpretation of the amplitude of stacked high‐frequency source radiations, which is commonly referred to as beam power, is still challenging since the analysis is not based on a forward model. In this article, we conduct a set of synthetic experiments to investigate the physical significance of back‐projection beam power. We find that beam power is mainly controlled by the spatial heterogeneity wavelength near the rupture front, rupture directivity, and the seismogram frequency. It is in contrast with some previous studies that link the beam power to the maximum slip rate (acceleration) amplitude near the rupture front. Based on the results, we develop a novel theoretical framework that can quantitatively interpret the frequency‐ and array‐dependent back‐projection results not only in our synthetic experiments, but also the 2019 bilateral rupture M7.6 New Ireland earthquake.
    Beschreibung: Key Points: We use kinematic forward models to investigate the relation between back‐projection beam location, power and earthquake source properties. Frequency‐dependent back‐projection peak beam power depends on the spatial heterogeneity near the rupture front, and rupture directivity. We develop a novel framework to analyze frequency‐ and array‐dependent back‐projection results, including the 2019 M7.6 New Ireland Event.
    Beschreibung: European Union's Horizon 2020 (ChEESE)
    Beschreibung: European Research Council (ERC)
    Beschreibung: German Research Foundation (DGF)
    Beschreibung: KAUST‐CRG
    Beschreibung: Leon and Joann V.C. Knopoff
    Beschreibung: NSF EAR
    Beschreibung: https://doi.org/10.7914/SN/AK
    Beschreibung: https://doi.org/10.7914/SN/AT
    Beschreibung: https://doi.org/10.7914/SN/AV
    Beschreibung: https://doi.org/10.7914/SN/BW
    Beschreibung: https://doi.org/10.7914/SN/CC
    Beschreibung: https://doi.org/10.7914/SN/CI
    Beschreibung: https://doi.org/10.7914/SN/CN
    Beschreibung: https://doi.org/10.7914/SN/II
    Beschreibung: https://doi.org/10.7914/SN/IU
    Beschreibung: https://doi.org/10.7914/SN/TA
    Beschreibung: https://doi.org/10.7914/SN/UW
    Schlagwort(e): ddc:551.22
    Sprache: Englisch
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  • 7
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    Historical Earthquakes, Paleoseismology, Neotectonics and Seismic Hazard: New Insights and Suggested Procedures (2020)
    Deutsche Gesellschaft für Erdbebeningenieurwesen und Baudynamik (DGEB) e.V. | Kiel
    Details
    Publikationsdatum: 2022-07-13
    Beschreibung: This publication developed from the 5th International Colloquium on “Historical Earthquakes, Paleoseismology, Neotectonics and Seismic Hazard” which was held from 11 to 13 October 2017 at the Federal Institute for Geosciences and Natural Resources (BGR) in Hannover, Germany. In this colloquium, 75 experts from 17 countries presented and discussed recent results, ongoing studies and planned projects on the topics historical earthquakes, macroseismology, archeoseismology, paleoseismology, earthquake catalogues and databases, active faults, seismotectonics, neotectonics, and seismic hazard assessment.
    Beschreibung: Deutsche Gesellschaft für Erdbebeningenieurwesen und Baudynamik
    Beschreibung: 〈b〉Introduction: Historical Earthquakes, Paleoseismology, Neotectonics and Seismic Hazard: New Insights and Suggested Procedures〈/b〉 〈br〉 〈i〉Diethelm Kaiser〈/i〉 〈br〉 〈a href="https://doi.org/10.23689/fidgeo-3868"〉 DOI: https://doi.org/10.23689/fidgeo-3868〈/a〉〈br〉 〈br〉〈/br〉 〈b〉Best practice of macroseismic intensity assessment applied to the earthquake catalogue of southwestern Germany〈/b〉 〈br〉 〈i〉 Wolfgang Brüstle, Uwe Braumann, Silke Hock and Fee-Alexandra Rodler 〈/i〉〈br〉 〈a href="https://doi.org/10.23689/fidgeo-3864"〉 DOI:https://doi.org/10.23689/fidgeo-3864〈/a〉〈br〉 〈br〉〈/br〉 〈b〉The earthquake of September 3, 1770 near Alfhausen (Lower Saxony, Germany): a real, doubtful, or a fake event? 〈/b〉 〈br〉 〈i〉Günter Leydecker and Klaus Lehmann 〈/i〉 〈br〉〈a href="https://doi.org/10.23689/fidgeo-3865"〉 DOI: https://doi.org/10.23689/fidgeo-3865〈/a〉〈br〉 〈br〉〈/br〉 〈b〉How well does known seismicity between the Lower Rhine Graben and southern North Sea reflect future earthquake activity? 〈/b〉 〈br〉 〈i〉Thierry Camelbeeck, Kris Vanneste, Koen Verbeeck, David Garcia-Moreno, Koen Van Noten and Thomas Lecocq 〈/i〉 〈br〉〈a href="https://doi.org/10.23689/fidgeo-3866"〉 DOI: https://doi.org/10.23689/fidgeo-3866〈/a〉〈br〉 〈br〉〈/br〉 〈b〉The Paleoseismic Database of Germany and Adjacent Regions PalSeisDB v1.0〈/b〉〈br〉 〈i〉Jochen Hürtgen, Klaus Reicherter, Thomas Spies, Claudia Geisler and Jörg Schlittenhardt 〈/i〉 〈br〉〈a href="https://doi.org/10.23689/fidgeo-3867"〉 DOI: https://doi.org/10.23689/fidgeo-3867〈/a〉〈br〉
    Beschreibung: research
    Schlagwort(e): ddc:551.22 ; ddc:554.3 ; ddc:550
    Sprache: Englisch
    Materialart: doc-type:book
    Format: 135
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  • 8
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    Seismic Velocity Recovery in the Subsurface: Transient Damage and Groundwater Drainage Following the 2015 Gorkha Earthquake, Nepal (2022)
    Details
    Publikationsdatum: 2022-09-22
    Beschreibung: Shallow earthquakes frequently disturb the hydrological and mechanical state of the subsurface, with consequences for hazard and water management. Transient post‐seismic hydrological behavior has been widely reported, suggesting that the recovery of material properties (relaxation) following ground shaking may impact groundwater fluctuations. However, the monitoring of seismic velocity variations associated with earthquake damage and hydrological variations are often done assuming that both effects are independent. In a field site prone to highly variable hydrological conditions, we disentangle the different forcing of the relative seismic velocity variations δv retrieved from a small dense seismic array in Nepal in the aftermath of the 2015 Mw 7.8 Gorkha earthquake. We successfully model transient damage effects by introducing a universal relaxation function that contains a unique maximum relaxation timescale for the main shock and the aftershocks, independent of the ground shaking levels. Next, we remove the modeled velocity from the raw data and test whether the corresponding residuals agree with a background hydrological behavior we inferred from a previously calibrated groundwater model. The fitting of the δv data with this model is improved when we introduce transient hydrological properties in the phase immediately following the main shock. This transient behavior, interpreted as an enhanced permeability in the shallow subsurface, lasts for ∼6 months and is shorter than the damage relaxation (∼1 yr). Thus, we demonstrate the capability of seismic interferometry to deconvolve transient hydrological properties after earthquakes from non‐linear mechanical recovery.
    Beschreibung: Plain Language Summary: Earthquake ground shaking damage the rocks in the subsurface of the Earth, altering their strength and their permeability. After the main shock, the rock properties slowly return to their pre‐earthquake state, but the duration of this recovery is poorly constrained. One way to investigate these time‐dependent changes is through the monitoring of seismic velocity inferred from ambient ground vibration recorded at seismic stations. Here, we constrain the evolution of seismic velocity following the large 2015 Mw 7.8 Gorkha earthquake in Nepal, in a field site characterized by seasonal groundwater fluctuations. We find that the velocity recoveries after the main shock and the aftershocks can be modeled with the same recovery timescale, independently from the initial shaking intensity. This suggests that earthquakes of different sizes activate the same geological structures and mechanisms during the recovery phase. Thanks to the unique hydrological setting of our field site and a model that links seismic velocity and groundwater level, we also show that this change of rock properties after the main shock is accompanied by a transient change in hydrological properties, an observation inferred for the first time with seismic measurement.
    Beschreibung: Key Points: We estimate a recovery time scale (〈1 yr) in seismic velocity changes after the Gorkha earthquake using ambient noise correlations. Velocity recoveries are modeled with relaxation functions characterized by a constant maximum relaxation timescale that is peak ground velocity‐independent. We highlight a transient enhanced permeability from the velocity changes in the first ∼6 months following the main shock.
    Beschreibung: GFZ HART program
    Beschreibung: https://doi.org/10.5880/GFZ.4.6.2021.002
    Beschreibung: https://doi.org/10.14470/KA7560056170
    Schlagwort(e): ddc:551.22
    Sprache: Englisch
    Materialart: doc-type:article
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