scholarly journals Modelling high-frequency seismograms at ocean bottom seismometers: effects of heterogeneous structures on source parameter estimation for small offshore earthquakes and shallow low-frequency tremors

2020 ◽  
Vol 223 (3) ◽  
pp. 1708-1723
Author(s):  
Shunsuke Takemura ◽  
Suguru Yabe ◽  
Kentaro Emoto
Keyword(s):  
Wave Propagation ◽  
Parameter Estimation ◽  
Seismic Wave ◽  
High Frequency ◽  
Source Parameters ◽  
Low Frequency ◽  
Accretionary Prism ◽  
Seismic Wave Propagation ◽  
Source Parameter ◽  
Seismic Events

SUMMARY The source characteristics of offshore seismic events, especially regular (or fast) and slow earthquakes, can provide key information on their source physics and frictional conditions at the plate boundary. Due to strong 3-D heterogeneities in offshore regions, such as those relating to sea water, accretionary prism and small-scale velocity heterogeneity, conventional methods using a 1-D earth model may mis-estimate source parameters such as the duration and radiation energy. Estimations could become severe inaccuracies for small offshore seismic events because high-frequency (>1 Hz) seismograms, which are strongly affected by 3-D heterogeneities, are only available for analysis because of their signal-to-noise ratio. To investigate the effects of offshore heterogeneities on source parameter estimation for small seismic events, we analysed both observed and simulated high-frequency seismograms southeast off the Kii Peninsula, Japan, in the Nankai subduction zone. Numerical simulations of seismic wave propagation using a 3-D velocity structure model clarified the effects of each heterogeneity. Comparisons between observations and model simulations demonstrated that the thick low-velocity accretionary prism has significant effects on high-frequency seismic wave propagation. Especially for shallow low-frequency tremors occurring at depths just below the accretionary prism toe, seismogram durations are significantly broader than an assumed source duration, even for stations with epicentral distances of approximately 10 km. Spindle-shape seismogram envelopes were observed even at such close stations. Our results suggest that incorporating 3-D heterogeneities is necessary for practical estimation of source parameters for small offshore events.

The effect of Yucca Fault on seismic wave propagation

1971 ◽  
Vol 61 (3) ◽  
pp. 697-706 ◽  
Author(s):  
Walter W. Hays ◽  
John R. Murphy
Keyword(s):  
Wave Propagation ◽  
Seismic Wave ◽  
Seismic Waves ◽  
Low Frequency ◽  
Test Site ◽  
Seismic Wave Propagation ◽  
Nevada Test Site ◽  
Basement Rocks ◽  
Geological Discontinuity ◽  
Frequency Components

abstract Yucca Fault is a major structural feature of Yucca Flat, a well-known geological province of the Nevada Test Site (NTS). The trace of the Fault extends north-south over a distance of about 32 km. The fault plane is nearly vertical and offsets Quaternary alluvium, Tertiary volcanic tuffs and pre-Cenozoic basement rocks (quartzites, shales and dolomites) with relative down displacement of several hundred feet on the east side of the fault. Data recorded from the CUP underground nuclear detonation in Yucca Flat typify the effect of the fault on near-zone (i.e., inside 10 km) seismic wave propagation. The effect of the fault is frequency dependent. It affects the frequency components (3.0, 5.0, 10.0 Hz) of the seismic waves which have characteristic wavelengths in the order of the geological discontinuity. Little or no effect is observed for low-frequency components (0.5, 1.0 Hz) which have wave-lengths exceeding the dimensions of the geological discontinuity. The effect of the fault does not represent a safety problem.

Modeling of Seismic Wave Propagation at Tiris Geothermal Area Using 2D Spectral Element Method (SEM)

2015 ◽  
Vol 771 ◽  
pp. 257-260 ◽  
Author(s):  
Agus Suprianto ◽  
Wahyudi ◽  
Wiwit Suryanto ◽  
Agus Subekti
Keyword(s):  
Wave Propagation ◽  
Seismic Wave ◽  
Spectral Element Method ◽  
Source Parameters ◽  
Spectral Element ◽  
Seismic Wave Propagation ◽  
Geological Model ◽  
Geothermal Area ◽  
Earthquake Source Parameters ◽  
Element Method

The spectral-element method (SEM) has been applied to simulate seismic wave propagation in 2D tentative geological model of Geothermal Area in Tiris, East Java Indonesia. we used 2-D model with 36 km x 5 km dimensions and discretized into 720 × 80 rectangular elements (mesh). We computed 8000 time steps with a sampling interval of 0.001 s using 10 Hz Ricker wavelet. The snapshots of seismic wave propagation along Tiris 2D geological model illustrate that SEM could accurately modeling seismic wave propagation. The seismic event that triggers a vibration in rock layers not only depend on the characteristics of the seismic earthquake source parameters and seismic wave propagation media, but also influenced by geometry of the media, such as topography and geological setting. The influence of ground topography, difference media, and structural geology were demonstrated by different time of wave arrival and different amplitudes. Therefore, SEM could be applied as preliminary study in geothermal exploration.

scholarly journals Oceanic high-frequency global seismic wave propagation with realistic bathymetry

2020 ◽  
Vol 222 (2) ◽  
pp. 1178-1194
Author(s):  
Benjamin Fernando ◽  
Kuangdai Leng ◽  
Tarje Nissen-Meyer
Keyword(s):  
Wave Propagation ◽  
Seismic Wave ◽  
High Frequency ◽  
Seismic Wave Propagation ◽  
Global Ocean ◽  
Data Sets ◽  
Ocean Bottom ◽  
Seafloor Topography ◽  
Ocean Loading ◽  
Ocean Layer

SUMMARY We present a new approach to simulate high-frequency seismic wave propagation in and under the oceans. Based upon AxiSEM3D, this method supports a fluid ocean layer, with associated water-depth phases and seafloor topography (bathymetry). The computational efficiency and flexibility of this formulation means that high-frequency calculations may be carried out with relatively light computational loads. A validation of the fluid ocean implementation is shown, as is an evaluation of the oft-used ocean loading formulation, which we find breaks down at longer periods than was previously believed. An initial consideration of the effects of seafloor bathymetry on seismic wave propagation is also given, wherein we find that the surface waveforms are significantly modified in both amplitude and duration. When compared to observed data from isolated island stations in the Pacific, synthetics which include a global ocean and seafloor topography appear to more closely match the observed waveform features than synthetics generated from a model with topography on the solid surface alone. We envisage that such a method will be of use in understanding the new and exciting ocean-bottom and floating seismometer data sets now being regularly collected.

Sign in / Sign up

Export Citation Format

Share Document