scholarly journals Observation of the long-period monotonic seismic waves of the November 11, 2018, Mayotte event by Iranian broadband seismic stations

2021 ◽  
Vol 73 (1) ◽  
Author(s):  
Hossein Sadeghi ◽  
Sadaomi Suzuki
Keyword(s):  
Surface Waves ◽  
Seismic Waves ◽  
Maximum Amplitude ◽  
Body Waves ◽  
Dipole Source ◽  
Arrival Times ◽  
Unusual Event ◽  
Long Period ◽  
Clear Peak ◽  
The Difference

AbstractOn November 11, 2018, an event generating long-lasting, monotonic long-period surface waves was observed by seismographs around the world. This event occurred at around 09:28 UTC east of the Mayotte Island, in the Indian Ocean off the coast of East Africa. This event is unusual due to the absence of body waves in the seismograms and no feeling of earth shaking by people locally. The purpose of this study is to investigate this unusual event using the waveforms recorded by 26 stations of the Iranian National Broadband Seismic Network. The stations are located at epicentral distances ranging from 4542 to 5772 km north-northeast of the event’s epicenter. The arrival of monochromatic long-period signals is visible around 10 UTC in the recordings of all the stations and the signals lasted for more than 30 min. Frequency analysis of the seismograms shows a clear peak at 0.064 Hz (15.6 s/cycle). The maximum amplitude of the transverse components is less than a half of the radial components. This is in agreement with the theoretical radiation pattern of Rayleigh and Love waves at a frequency of 0.06 Hz for a vertical compensated linear vector dipole source mechanism. The average apparent phase velocities were calculated as 3.31 and 2.97 km/s, in the transverse and radial directions, corresponding, respectively, to Love and Rayleigh waves in the frequency range of 0.05–0.07 Hz. A surface wave magnitude of Ms 5.07 ± 0.22 was estimated. Just before the monochromatic signal arrives, there is some dispersion in the surface waves. This observation may suggest a regular earthquake of Ms 4.3 ± 0.11 that triggered the November 11, 2018, event. The difference between the arrival times of the recorded surface waves of the two events is estimated to be less than 31 s, and most likely of ~ 7 s only.

scholarly journals Observation of the Long-Period Monotonic Seismic Waves of the November 11, 2018, Mayotte event by the Iranian Broadband Seismic Stations

2020 ◽  
Author(s):  
Hossein Sadeghi ◽  
Sadaomi Suzuki
Keyword(s):  
Surface Waves ◽  
Rayleigh Waves ◽  
Seismic Waves ◽  
Maximum Amplitude ◽  
Body Waves ◽  
Unusual Event ◽  
Long Period ◽  
Phase Velocities ◽  
Clear Peak ◽  
Rayleigh And Love Waves

Abstract On November 11, 2018, an event generating long-lasting, monotonic long-period surface waves was observed by seismographs around the world. This event occurred at around 09:30 (UTC) east of the Mayotte Island, east Africa. This event is unusual due to the absence of body waves in the seismograms and people’s lack of sense. The purpose of this study is to investigate this unusual event using the waveforms recorded by the Iranian National Broadband Seismic Network. The network consisted of 26 stations in operation on November 11, 2018. The stations are located from 4542 km to 5772 km north-northeast of the event’s epicentre. The arrival of monochromatic long-period signals is visible around 10 UTC in the recordings of all the stations and lasts for more than 30 minutes. Frequency analysis of the seismograms shows a clear peak at 0.064 Hz (15.6 sec/cycle). The maximum amplitude of the transverse components is less than a half of the radial components. This is in agreement with the theoretical radiation pattern of Rayleigh and Love waves at a frequency of 0.06 Hz from a vertical Compensated Linear Vector Dipole (CLVD) source mechanism. The average apparent phase velocities are calculated as 3.31 km/s and 2.97 km/s, in the transverse and radial directions, corresponding respectively to the Love and Rayleigh waves in the range of 0.05 to 0.07 Hz. The surface wave magnitude of Ms 5.07 ± 0.22 was estimated. Just before the monochromatic signal, there is some dispersion in the surface waves. This observation may suggest a regular earthquake that triggered the strange Mayotte event.

The rupture process and aftershock distribution of the 6 April 1992 MS 6.8 earthquake, Offshore British Columbia

1995 ◽  
Vol 85 (3) ◽  
pp. 716-735 ◽  
Author(s):  
John F. Cassidy ◽  
Garry C. Rogers
Keyword(s):  
Surface Waves ◽  
Triple Junction ◽  
Rupture Process ◽  
Body Waves ◽  
Ocean Bottom Seismometer ◽  
Strain Accumulation ◽  
Transform Fault ◽  
Junction Region ◽  
Long Period ◽  
Initial Rupture

Abstract On 6 April 1992, a magnitude 6.8 (MS) earthquake occurred in the triple-junction region at the northern end of the Cascadia subduction zone. This was the largest earthquake in at least 75 yr to occur along the 110-km-long Revere-Dellwood-Wilson (RDW) transform fault and the first large earthquake in this region recorded by modern broadband digital seismic networks. It thus provides an opportunity to examine the rupture process along a young (<2 Ma) oceanic transform fault and to gain better insight into the tectonics of this triple-junction region. We have investigated the source parameters and the rupture process of this earthquake by modeling broadband body waves and long-period surface waves and by accurately locating the mainshock and the first 10 days of aftershocks using a well-located “calibration” event recorded during an ocean-bottom seismometer survey. Analysis of P and SH waveforms reveals that this was a complex rupture sequence consisting of three strike-slip subevents in 12 sec. The initial rupture occurred 5 to 6 km to the SW of the seafloor trace of the RDW fault at 50.55° N, 130.46° W. The dominant subevent occurred 2 to 3 sec later and 4.3 km beneath the seafloor trace of the RDW fault, and a third subevent occurred 5 sec later, 18 km to the NNW, suggesting a northwestward propagating rupture. The aftershock sequence extended along a 60- to 70-km-long segment of the RDW fault, with the bulk of the activity concentrated ∼30 to 40 km to the NNW of the epicenter, consistent with this interpretation. The well-constrained mechanism of the initial rupture (strike/dip/slip 339°/90°/−168°) and of the largest aftershock (165°/80°/170°) are rotated 15° to 20° clockwise relative to the seafloor trace of the RDW fault but are parallel to the Pacific/North America relative plate motion vector. In contrast, the mechanisms of the dominant subevent (326°/87°/−172°), and the long-period solution derived from surface waves aligns with the RDW fault. This suggests that small earthquakes (M < 6) in this area occur along faults that are optimally aligned with respect to the regional stress field, whereas large earthquakes, involving tens of kilometers of rupture, activate the RDW fault. For the mainshock, we estimate a seismic moment (from surface waves) of 1.0 × 1026 dyne-cm, a stress drop of 60 bars, and an average slip of 1.2 m. This represents only 21 yr of strain accumulation, implying that there is either a significant amount of aseismic slip along the RDW fault or that much of the strain accumulation manifests itself as deformation within the Dellwood and Winona blocks or along the continental margin.

Observations of Loma Prieta aftershocks from a dense array in Sunnyvale, California

1991 ◽  
Vol 81 (5) ◽  
pp. 1900-1922
Author(s):  
Arthur Frankel ◽  
Susan Hough ◽  
Paul Friberg ◽  
Robert Busby
Keyword(s):  
Surface Waves ◽  
Body Waves ◽  
Love Waves ◽  
Apparent Velocity ◽  
Dense Array ◽  
S Wave ◽  
Small Aperture ◽  
Long Period ◽  
Santa Clara Valley ◽  
Loma Prieta

Abstract A small aperture (≈300 m), four-station array was deployed in Sunnyvale, California for 5 days to record aftershocks of the Loma Prieta earthquake of October 1989. The purpose of the array was to study the seismic response of the alluvium-filled Santa Clara Valley and the role of surface waves in the seismic shaking of sedimentary basins. Strong-motion records of the Loma Prieta mainshock indicate that surface waves produced the peak velocities and displacements at some sites in the Santa Clara Valley. We use the recordings from the dense array to determine the apparent velocity and azimuth of propagation for various arrivals in the seismograms of four aftershocks with magnitudes between 3.6 and 4.4. Apparent velocities are generally observed to decrease with increasing time after the S wave in the seismograms. Phases arriving less than about 8 sec after the S wave have apparent velocities comparable to the S wave and appear to be body waves multiply reflected under the receiver site or reflected by crustal interfaces. For times 10 to 30 sec after the direct S wave, we observe long-period (1 to 6 sec) arrivals with apparent velocities decreasing from 2.5 to 0.8 km / sec. We interpret these arrivals to be surface waves and conclude that these surface waves produce the long duration of shaking observed on the aftershock records. Much of the energy in the 40 sec after the S-wave is coming approximately from the direction of the source, although some arrivals have backazimuths as much as 60° different from the backazimuths to the epicenters. Two of the aftershocks show arrivals coming from 30 to 40° more easterly than the epicenters. This energy may have been scattered from outcrops along the southeastern edge of the basin. In contrast, the deepest aftershock studied (d = 17 km) displays later arrivals with backazimuths 30 to 40° more westerly than the epicenter. A distinct arrival for one of the aftershocks propagates from the southwest, possibly scattered from the western edge of the basin. Synthetic seismograms derived from a plane-layered crustal model do not produce the long-period Love waves observed in the waveforms of the ML 4.4 aftershock. These Love waves may be generated by the conversion of incident S waves or Rayleigh waves near the edge of the basin.

scholarly journals DETERMINATION OF EARTHQUAKE FOCUS COORDINATES USING THE CASSINI OVAL METHOD WITH SECOND- AND FOURTH-ORDER HYPERBOLA FIGURES

2020 ◽  
Vol 46 (4) ◽  
pp. 134-142
Author(s):  
B. I. Shakhtarin ◽  
T. G. Aslanov ◽  
U. R. Tetakaev
Keyword(s):  
Comparative Analysis ◽  
Fourth Order ◽  
Relative Position ◽  
Seismic Waves ◽  
Arrival Times ◽  
Earthquake Focus ◽  
Seismic Sensors ◽  
Calculation Results ◽  
The Difference

Objectives. To study the dependencies obtained when determining the coordinates of an earthquake hypocentre using the figures of fourth and second orders.Method. A comparative analysis of determining the coordinates of the earthquake focus using the Cassini oval method, both taking errors in the readings of seismic sensors into account the and ignoring them, is presented.Result. A new method is proposed for determining the coordinates of the earthquake hypocentre, which uses the fourth-order figure, the Cassini oval, in the calculations. A graph is obtained for the distribution of errors in determining the coordinates of the earthquake focus (using the Cassini oval) depending on the relative position of two seismic sensors with different values of their errors in determining the difference in travel times of seismic waves.Conclusion. Since the calculation results are independent of the error sign in determining the difference in the arrival times of seismic waves, the method is suitable for the initial determination of the coordinates of the earthquake hypocentre as well as for comparison with the results of other methods for identifying the error sign. 

scholarly journals Teleseismic source parameters and rupture characteristics of the 24 November 1987, Superstition Hills earthquake

1990 ◽  
Vol 80 (1) ◽  
pp. 43-56 ◽  
Author(s):  
Lorraine J. Hwang ◽  
Harold Magistrale ◽  
Hiroo Kanamori
Keyword(s):  
Source Parameters ◽  
Seismic Source ◽  
Point Sources ◽  
Body Waves ◽  
Rupture Velocity ◽  
Total Moment ◽  
Long Period ◽  
The North ◽  
The Difference ◽  
Northern Segment

Abstract Long-period body waves from the 24 November 1987, Superstition Hills earthquake are studied to determine the focal mechanism and spatial extent of the seismic source. The earthquake is a complex event consisting of two spatially distinct subevents with different focal mechanisms. Two consistent models of rupture are developed. For both models, the second subevent begins 8 sec after the initiation of the first subevent and the preferred centroid depth lies between 4 to 8 km. Model 1 consists of two point sources separated by 15 to 20 km along strike of the Superstition Hills fault. Model 2 consists of one point source and one line source with a rupture velocity of 2.5 km/sec with moment release distributed along strike of the focal plane at a distance of 10 to 22 km from the epicenter. These moment release patterns show that a significant amount of long-period energy is radiated from the southern segment of the fault. Total moment release for both models is approximately 8 × 1025 dyne-cm. Both models also suggest a change of dip from near vertical near the epicenter to steeply southwesterly dipping along the southern segment of the fault. The difference in rupture characteristics and fault dips seen teleseismically is also reflected in aftershock and afterslip data, and crustal structure underlying the two fault segments. The northern segment had more aftershocks and a smaller proportion of afterslip than the southern segment. The boundary between the two segments lies at a step in the basement that separates a deeper metasedimentary basement to the south from a shallower crystalline basement to the north.

Large Explosions at Sea

1971 ◽  
Vol 8 (2) ◽  
pp. 243-247
Author(s):  
Goetz G. R. Buchbinder
Keyword(s):  
Surface Wave ◽  
Continental Shelf ◽  
Surface Waves ◽  
Small Amplitude ◽  
Body Wave ◽  
Surface Wave Magnitude ◽  
Underwater Explosions ◽  
Long Period ◽  
Short Period ◽  
The Difference

Two large unannounced events occurred at sea in aseismic areas in the Atlantic. Comparison of these with the announced event Chase III shows them to be explosions.Large explosions at sea may be recognized by the relatively small amplitude of long period surface waves with periods up to 10 s. Energy of longer periods is absent for events mb ≤ 5.5. The surface wave magnitudes for the events are at least 1.5 smaller at 10 s than those of underground explosions of equal mb, at 20 s they are at least 0.9 smaller. At longer periods the difference between body wave and surface wave magnitude is larger than 0.9 but larger explosions are needed to determine the separation. Underwater explosions on or near the continental shelf are very efficient in the generation of higher mode short period waves.

The Nature of Intrinsic Attenuation

2020 ◽  
Author(s):  
Yu-Chang Wu ◽  
Cheng-Ju Wu
Keyword(s):  
Seismic Waves ◽  
Body Waves ◽  
Northwestern Pacific ◽  
The Novel ◽  
Low Velocity ◽  
High Attenuation ◽  
Intrinsic Attenuation ◽  
Novel Method ◽  
The Difference ◽  
The Relationship

<p>Intrinsic attenuation plays an important role in investigating the interior structure of Earth, especially for the Lithosphere-asthenosphere system, the best place to understand the physical mechanics of plate tectonic. The dissipation, the high attenuation of seismic waves in the low-velocity zones, and the frequency dependence are the characteristic of intrinsic attenuation. However, N. Takeuchi, et al. measured the Northwestern Pacific Ocean’s lithosphere-asthenosphere system, and state the attenuation of the asthenosphere is 50 times larger than the attenuation of lithosphere attenuation. The attenuation of the lithosphere shows strong frequency dependency, but the attenuation of the asthenosphere does not. Previous theories of attenuation failed to explain this phenomenon. Here we demonstrate an explicit attenuation formulation to explain the high attenuation of seismic waves in the low-velocity zones and to show the mechanisms of spectral of teleseismic body waves rapidly fall off as frequency bigger than 1 Hz by perturbing the wave equation with the novel method we proposed. The result also indicates that the difference between the attenuation of the lithosphere and asthenosphere is because their attenuation governs by different physics mechanisms and mathematical models. Moreover, we illustrate the explicit formulation of the relationship between apparent t*, wave velocity, and frequency.</p>

scholarly journals Modeling P waves in seismic noise correlations: Application to fault monitoring using train traffic sources

2021 ◽  
Author(s):  
Korbinian Sager ◽  
Victor Tsai ◽  
Yixiao Sheng ◽  
Florent Brenguier ◽  
Pierre Boué ◽  
...  
Keyword(s):  
Green’S Function ◽  
Surface Waves ◽  
Green's Function ◽  
Seismic Waves ◽  
Low Frequency ◽  
Body Waves ◽  
Noise Sources ◽  
P Waves ◽  
Promising Alternative ◽  
Fault Monitoring

The theory of Green's function retrieval essentially requires homogeneously distributed noise sources. Even though these conditions are not fulfilled in nature, low-frequency (<1 Hz) surface waves generated by ocean-crust interactions have been used successfully to image the crust with unprecedented spatial resolution. In contrast to low-frequency surface waves, high-frequency (>1 Hz) body waves have a sharper, more localized sensitivity to velocity contrasts and temporal changes at depth. In general, their retrieval using seismic interferometry is challenging, and recent studies focus on powerful, localized noise sources. They have proven to be a promising alternative but break the assumptions of Green's function retrieval. In this study, we present an approach to model correlations between P waves for these scenarios and analyze their sensitivity to 3D Earth structure. We perform a series of numerical experiments to advance our understanding of these signals and prepare for an application to fault monitoring. In the considered cases, the character of the signals strongly diverges from Green's function retrieval, and the sensitivity to structure has significant contributions in the source direction. An accurate description of the underlying physics allows us to reproduce observations made in the context of monitoring the San Jacinto Fault in California using train-generated seismic waves. This approach provides new perspectives for detecting and localizing temporal velocity changes previously unnoticed by commonly exploited surface-wave reconstructions.

scholarly journals Calving localization at Helheim Glacier using multiple local seismic stations

2017 ◽  
Vol 11 (1) ◽  
pp. 609-618 ◽  
Author(s):  
M. Jeffrey Mei ◽  
David M. Holland ◽  
Sridhar Anandakrishnan ◽  
Tiantian Zheng
Keyword(s):  
Surface Wave ◽  
Wave Velocity ◽  
Rayleigh Waves ◽  
Seismic Waves ◽  
Grid Search ◽  
Arrival Times ◽  
S Waves ◽  
Surface Wave Velocity ◽  
The Difference ◽  
Wave Arrival

Abstract. A multiple-station technique for localizing glacier calving events is applied to Helheim Glacier in southeastern Greenland. The difference in seismic-wave arrival times between each pairing of four local seismometers is used to generate a locus of possible event origins in the shape of a hyperbola. The intersection of the hyperbolas provides an estimate of the calving location. This method is used as the P and S waves are not distinguishable due to the proximity of the local seismometers to the event and the emergent nature of calving signals. We find that the seismic waves that arrive at the seismometers are dominated by surface (Rayleigh) waves. The surface-wave velocity for Helheim Glacier is estimated using a grid search with 11 calving events identified at Helheim from August 2014 to August 2015. From this, a catalogue of 11 calving locations is generated, showing that calving preferentially happens at the northern end of Helheim Glacier.

Travel times and amplitudes of principal body phases recorded from gnome

1962 ◽  
Vol 52 (5) ◽  
pp. 1057-1074 ◽  
Author(s):  
Carl Romney ◽  
Billy G. Brooks ◽  
Robert H. Mansfield ◽  
Dean S. Carder ◽  
James N. Jordan ◽  
...  
Keyword(s):  
United States ◽  
Seismic Waves ◽  
Test Site ◽  
The United States ◽  
Body Waves ◽  
Travel Times ◽  
Eastern United States ◽  
Nevada Test Site ◽  
Short Period ◽  
The Difference

abstract gnome, an undergound nuclear explosion in salt near Carlsbad, New Mexico, produced seismic waves which were recorded widely throughout the United States and at a few foreign stations. The travel times of P were strongly dependent on the path of propagation, and were as much as 12 seconds earlier in the eastern United States than at equivalent distances in the western part of the United States. At the few stations more distant than 25°, P was about 2 seconds earlier than predicted by the Jeffreys-Bullen table for surface focus. Amplitudes of Pn were similarly dependent upon the path of propagation; although the measurements showed great scatter, amplitudes to the east were generally larger than those to the west. Pn travel time and amplitude anomalies suggest a systematic relationship to crustal thickness. There is evidence from the difference in the speeds and attenuation rates that Lg and P are not transmitted along analogous paths through the crust. Short period body waves were two or three times larger than expected from an explosion of the same energy in tuff at the Nevada Test Site. Surface waves, however, were relatively weak compared with explosions of similar yield in tuff.

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