Rupture characteristics of the 2019 North Peru intraslab earthquake (Mw8.0)

2020 ◽  
Author(s):  
Martin Vallée ◽  
Raphaël Grandin ◽  
Jean-Mathieu Nocquet ◽  
Juan-Carlos Villegas ◽  
Sandro Vaca ◽  
...  
Keyword(s):  
Back Propagation ◽  
Low Frequency ◽  
Depth Range ◽  
Slab Geometry ◽  
Rupture Dynamics ◽  
Earthquake Rupture Dynamics ◽  
Teleseismic Data ◽  
Intraslab Earthquake ◽  
Hypocentral Location ◽  
Slab Bending

<p>According to GlobalCMT, the 2019/05/26 North Peru earthquake is the largest event since 1976 in the wide depth range between 70km and 550km. Its hypocentral location (at about 130km depth) inside the Nazca slab geometry, together with its normal focal mechanism, favor an origin related to slab bending. Owing to its magnitude and depth, this earthquake generated large coseismic displacements over a broad area, that were geodetically measured by InSAR and GNSS. By combining these observations with regional and teleseismic data, we invert for the rupture process of the event, and first focus on the actual focal plane. Inversion reveals that the steeper plane (dipping 55-60° to the East) is preferred. A clear northward propagation is also imaged, with rupture traveling ~200km in 60s, and with little extent in the dip direction. This narrow rupture aspect implies that the stress drop is significant, even if a simple duration-based measurement would not indicate so. These inversion results obtained at relatively low frequency (below 0.2Hz) are then thoroughly compared with back-propagation images obtained at higher frequency (at 0.5-4Hz), which also highlight the dominantly northward rupture propagation with an average rupture speed of about 3 km/s. Implication in terms of earthquake rupture dynamics and occurrence of such large intermediate depth earthquakes in slabs will finally be discussed.<br>    </p>

A closer look at the relationship between slab (un)bending and double seismic zone seismicity

2020 ◽  
Author(s):  
Christian Sippl ◽  
Timm John ◽  
Stefan Schmalholz
Keyword(s):  
Steady State ◽  
Focal Mechanisms ◽  
Depth Range ◽  
Northern Chile ◽  
Slab Surface ◽  
Slab Geometry ◽  
Steady State Assumption ◽  
Slab Bending ◽  
State Assumption ◽  
Ne Japan

<p>The origin of double seismic zones (DSZs), parallel planes of intraslab seismicity observed in many subduction zones around the globe, is still highly debated. While most researchers assume that fluid release from prograde metamorphic reactions in the slab is an important control on DSZ occurrence, the role of slab unbending is currently unclear.<br>Slab bending at the outer rise is instrumental in hydrating the downgoing oceanic plate through bend faulting, and is evident from earthquake focal mechanisms (prevalence of shallow normal faulting events). Observations from NE Japan show that focal mechanisms of DSZ earthquakes are downdip compressive in the upper and downdip extensive in the lower plane of the DSZ, which strongly hints at slab unbending. This coincidence of slab unbending and DSZ seismicity in NE Japan has given rise to several models in which unbending forces are a prerequisite for DSZ occurrence.</p><p>To globally test a potential correlation of slab unbending with DSZ seismicity, we derived downdip slab surface curvatures on trench-perpendicular profiles every 50 km along all major oceanic slabs using the slab2 grids of slab surface depth. We here make a steady-state assumption, i.e. we assume that the slab geometry is relatively constant with time, so that the downdip gradient of slab curvature corresponds to slab (un)bending. We compiled the loci and depth extent of all DSZ observations avalable in literature, and compare these to the slab bending or unbending estimates.</p><p>Preliminary results indicate that while there is a clear correspondence between the depth of slab unbending to DSZ seismicity in the Japan-Kurile slab, most other slabs do not show this correlation. Moreover, some DSZs deviate from the above-mentioned focal mechanism pattern and exhibit downdip extension in both planes (e.g. Northern Chile, New Zealand). It appears that the global variability of slab geometries in the depth range 50-200 km is larger than anticipated, and DSZ seismicity is not limited to slabs where unbending is prevalent at these depths. The Northern Chile case is especially interesting because focal mechanisms there not only do not fit the pattern observed in NE Japan, but also can not be explained with the current slab geometry alone. This could indicate a direct influence of ongoing metamorphic reactions on focal mechanisms (e.g. via volume reduction and densification), or it may be a hint that our steady-state assumption is invalid for the Nazca slab here (i.e. that it is in the process of changing its geometry).</p>

Shallow subsurface mapping by electromagnetic sounding in the 300 kHz to 30 MHz range: Model studies and prototype system assessment

Geophysics ◽  
1994 ◽  
Vol 59 (8) ◽  
pp. 1201-1210 ◽  
Author(s):  
Duff C. Stewart ◽  
Walter L. Anderson ◽  
Thomas P. Grover ◽  
Victor F. Labson
Keyword(s):  
Dielectric Permittivity ◽  
High Frequency ◽  
Low Frequency ◽  
Computer Programs ◽  
Thin Layers ◽  
Depth Range ◽  
Frequency Range ◽  
Model Studies ◽  
New Instrument ◽  
Displacement Currents

A new instrument designed for frequency‐domain sounding in the depth range 0–10 m uses short coil spacings of 5 m or less and a frequency range of 300 kHz to 30 MHz. In this frequency range, both conduction currents (controlled by electrical conductivity) and displacement currents (controlled by dielectric permittivity) are important. Several surface electromagnetic survey systems commonly used (generally with frequencies less than 60 kHz) are unsuitable for detailed investigation of the upper 5 m of the earth or, as with ground‐penetrating radar, are most effective in relatively resistive environments. Most computer programs written for interpretation of data acquired with the low‐frequency systems neglect displacement currents, and are thus unsuited for accurate high‐frequency modeling and interpretation. New forward and inverse computer programs are described that include displacement currents in layered‐earth models. The computer programs and this new instrument are used to evaluate the effectiveness of shallow high‐frequency soundings based on measurement of the tilt angle and the ellipticity of magnetic fields. Forward model studies indicate that the influence of dielectric permittivity provides the ability to resolve thin layers, especially if the instrument frequency range can be extended to 50 MHz. Field tests of the instrument and the inversion program demonstrate the potential for detailed shallow mapping wherein both the resistivity and the dielectric permittivity of layers are determined. Although data collection and inversion are much slower than for low‐frequency methods, additional information is obtained inasmuch as there usually is a permittivity contrast as well as a resistivity contrast at boundaries between different materials. Determination of dielectric permittivity is particularly important for hazardous waste site characterization because the presence of some contaminants may have little effect on observed resistivity but a large effect on observed permittivity.

Seismic Body-Wave Tomography in Fennoscandia

2021 ◽  
Author(s):  
Nevra Bulut ◽  
Valerie Maupin ◽  
Hans Thybo
Keyword(s):  
Velocity Structure ◽  
Body Wave ◽  
Low Frequency ◽  
General Purpose ◽  
Depth Range ◽  
Quality Of Data ◽  
S Waves ◽  
Velocity Models ◽  
The North ◽  
Wave Tomography

<p><span>We present a seismic tomographic image of Fennoscandia based on data from the ScanArray project in Norway, Sweden, and Finland, which operated during 2012-2017, together with data from earlier projects and stationary stations. We use relative traveltime residuals of P- and S- waves in high- and low-frequency bands and apply the frequency-dependent crustal correction. We use seismic signals from earthquakes at epicentral distances between 30° and 104° and magnitudes larger than 5.5. The general purpose of this study is to understand the possible causes of the high topography in Scandinavia along the passive continental margins in the North Atlantic as well as the interrelation between structure at the surface and in the lithospheric mantle.</span></p><p><span>We present an upper-mantle velocity structure for most Fennoscandia derived for the depth range 50-800 km with a 3D multiscale parameterization for an inversion mesh-grid with dimensions </span><em><span>dx</span></em><span>=</span><em><span>dy</span></em><span>=17.38 km and </span><em><span>dz</span></em><span>=23.44 km. In all body-wave tomography methods, smearing of anomalies is expected. Therefore resolution tests are critical for assessing the resolution of the parameters determined in the velocity models. The resolution of the models depends on several factors, including the noise level and general quality of data, the density of observations, the distance and back-azimuthal distribution of sources, the damping applied, and the model parameterization. We use checkerboard and model-driven (block and cylindrical) tests for assessing the resolution of our models.</span></p><p><span>Seismic models derived in this study are compared to existing and past topography to contribute to understanding mechanisms responsible for the topographic changes in the Fennoscandian region. The models also provide a basis for deriving high-resolution models of temperature and compositional anomalies that may contribute to understanding the observed, enigmatic topography.</span></p>

scholarly journals Seismic observations with broadband instruments at Santorini volcano

2018 ◽  
Vol 40 (3) ◽  
pp. 1150 ◽  
Author(s):  
A. Kolaitis ◽  
P. Papadimiriou ◽  
I. Kassaras ◽  
K. Makropoulos
Keyword(s):  
Low Frequency ◽  
Volcanic Tremor ◽  
Velocity Model ◽  
Dominant Frequency ◽  
Depth Range ◽  
Traveltime Inversion ◽  
Time Frequency ◽  
Inversion Procedure ◽  
Santorini Volcano ◽  
Better Than

Two arrays equipped with broadband sensors were installed for a period of 10 months, in order to study the seismic activity in the area of Santorini (Thira) volcano. During these periods, about 330 earthquakes were recorded and located within a radius of 50 km from the center of the caldera. An iterative damped traveltime inversion procedure yielded a local 1-D Ρ-wave velocity model and improved locations with an accuracy better than 5 Km in both horizontal and vertical components for 135 earthquakes. Those are mainly distributed within a depth range 5-18 Km, in the vicinity of the submarine Kolumbo Reef (NE of Santorini Island). Signal analysis of the recorded volcanic earthquakes including typical Fourier transformations and several operations in the time-frequency domain, allowed their dominant frequency determination and their classification into three groups based on waveform appearance and frequency content: (1) highfrequency events; (2) low-frequency events; and (3) volcanic tremor. Frequencytime analysis of tremor, detected at three stations, revealed two kinds of harmonic tremor with one sharp peak, at 3-5 Hz and 8.5-10 Hz.

scholarly journals Fracture zones detection for groundwater exploration integrating Resistivity Profiling and Very Low Frequency electromagnetic methods (Errachidia basin, Morocco)

2019 ◽  
Vol 49 (2) ◽  
pp. 181-194
Author(s):  
Youssef Ait Bahammou ◽  
Ahmed Benamara ◽  
Abdellah Ammar ◽  
Ibrahim Dakir
Keyword(s):  
Low Frequency ◽  
Groundwater Exploration ◽  
Depth Range ◽  
Fracture Zones ◽  
Real Component ◽  
Very Low Frequency ◽  
Resistivity Measurements ◽  
Electromagnetic Methods ◽  
Groundwater Supply ◽  
Resistivity Profiling

Abstract Resistivity Profiling and Very Low Frequency (VLF) electromagnetic methods were introduced to study fracture zones detection in Zaouia Jdida locality, within the Errachidia basin. The Horizontal Profiling was conducted in Wenner-α array, with AB = 300 m and profile lines oriented NW–SE and NE–SW. The resistivity measurements were taken using MAE advanced geophysics instruments. The VLF profiles were implanted with the length reaches 1000 m and profile lines oriented in NE–SW direction. The VLF measurements were collected using T-VLF iris instrument and the data filtering was done using KHFFILT software. Two filters, Karous-Hjelt and Fraser, were applied to the real component of the secondary electromagnetic field. The qualitative interpretation of resistivity results, showed the presence of subsurface targets; fracture zones were detected at 70m, 240m and 450m positions along the profile P1, at 180m, 340m and 450m positions from the profile P2. The semi-quantitative interpretation of VLF results revealed the presence of two principal fracture zones at L3 and L5 locations, oriented NW–SE, at a depth range of 30 m to 60 m. The VLF anomaly observed at L3 location is confirmed by the resistivity measurements from the profile P1 (at 70m station). The identified fractures represent the potential zones for groundwater supply and then will have an implication on storage and movement of groundwater in the prospect area.

Evaluation of an Extended Operational Boussinesq-Type Wave Model for Calculating Low-Frequency Waves in Intermediate Depths

2011 ◽  
Author(s):  
Martijn P. C. de Jong ◽  
Mart Borsboom ◽  
Jan A. M. de Bont ◽  
Bas van Vossen
Keyword(s):  
Low Frequency ◽  
Wave Model ◽  
Coastal Engineering ◽  
Extended Model ◽  
Depth Range ◽  
Frequency Range ◽  
Frequency Wave ◽  
Type Wave ◽  
Wave Heights ◽  
Low Frequency Waves

The motions of (LNG) vessels moored offshore at depths ranging from about 20 to 100 m may depend significantly on the presence of (bound) low-frequency waves with periods in the order of 100 s. This is because these moored vessels show a large motion response in this frequency range and because the energy contents of low-frequency waves at these ‘intermediate’ depths is relatively large. As part of the Joint Industry Project HawaI, the operational Boussinesq-type wave model of Deltares, TRITON, was used to investigate whether this type of wave models could predict bound low-frequency waves (setdown waves) at intermediate depths. Comparison to measured and theoretical data, however, showed an underestimation of the computed levels of bound low-frequency wave heights for this depth range by a factor 2 to 4. Recently, additional tests were made with TRITON in situations for which the model has been designed: coastal engineering applications in shallow water (depths up to at most 20 m). These also showed an underestimation of the bound low-frequency wave heights, albeit smaller, up to a factor 2. In view of the importance of the energy contained in the low-frequency range for certain nearshore and shoreline processes, such as morphological processes, this underestimation is also of concern in coastal engineering. This triggered the development of a higher-order extension of the TRITON model equations (Borsboom, 2008, Wellens, 2010), with the aim to improve the accuracy of the model for long waves while still keeping computational times within acceptable (operational) limits. This paper reports on the usefulness of the extended model for the field of application considered in JIP HawaI/II: providing wave data for calculating the motions of vessels moored in intermediate depths. The results show a significant improvement of the modeling of nonlinear wave dynamics, including the prediction of bound low-frequency waves. This means that the model extension is an important step towards an operational Boussinesq-type wave model with sufficient accuracy in both the wave-frequency (sea, swell) and the low-frequency range for applications in intermediate depths.

Curved slickenlines preserve direction of rupture propagation

Geology ◽  
2019 ◽  
Vol 47 (9) ◽  
pp. 838-842
Author(s):  
Jesse Kearse ◽  
Yoshihiro Kaneko ◽  
Tim Little ◽  
Russ Van Dissen
Keyword(s):  
Cohesive Zone ◽  
Strike Slip ◽  
Rupture Propagation ◽  
Dynamic Rupture ◽  
Slip Direction ◽  
Rupture Dynamics ◽  
Earthquake Rupture Dynamics ◽  
Kaikoura Earthquake ◽  
Rupture Direction ◽  
Dextral Strike Slip

Abstract Slip-parallel grooves (striations) on fault surfaces are considered a robust indicator of fault slip direction, yet their potential for recording aspects of earthquake rupture dynamics has received little attention. During the 2016 Kaikōura earthquake (South Island, New Zealand), >10 m of dextral strike-slip on the steeply dipping Kekerengu fault exhumed >200 m2 of fresh fault exposure (free faces) where it crossed bedrock canyons. Inscribed upon these surfaces, we observed individual striae up to 6 m long, all of which had formed during the earthquake. These were typically curved. Using simulations of spontaneous dynamic rupture on a vertical strike-slip fault, we reproduce the curved morphology of striae on the Kekerengu fault. Assuming strike-slip pre-stress, our models demonstrate that vertical tractions induced by slip in the so-called cohesive zone result in transient changes in slip direction. We show that slip-path convexity is sensitive to the direction of rupture propagation. To match the convexity of striae formed in 2016 requires the rupture to have propagated in a northeast direction, a prediction that matches the known rupture direction of the Kaikōura earthquake. Our study highlights the potential for fault striae to record aspects of rupture dynamics, including the rupture direction of paleo strike-slip earthquakes.

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