Seismic signals preceding the explosive eruption of Mount St. Helens, Washington, on 18 May 1980

1983 ◽  
Vol 73 (6A) ◽  
pp. 1797-1813
Author(s):  
Anthony Qamar ◽  
William St. Lawrence ◽  
Johnnie N. Moore ◽  
George Kendrick
Keyword(s):  
Seismic Waves ◽  
Low Frequency ◽  
Seismic Energy ◽  
B Value ◽  
Volcanic Earthquake ◽  
Seismic Signals ◽  
Volcanic Earthquakes ◽  
Short Period ◽  
Stressed Region ◽  
Mount St Helens

Abstract The intense seismic activity which preceded the 18 May 1980 eruption of Mount St. Helens, Washington, released 2 to 3 × 1018 ergs/day in earthquakes that did not correlate temporally with phreatic eruptions which occurred during the same period. Although the b value and amplitude ratios (long-period/short-period) of the earthquakes vary with time, there are no definitive precursors to the 18 May earthquake and eruption. A Mogi type II frequency-magnitude relation, with critical magnitude Mc = 4.6, constrains the characteristic dimension of the highly stressed region under Mount St. Helens to approximately 3 km, preceding the eruption. A major increase in seismic energy release and a decrease in b value around 1 April 1980 may indicate the first major influx of magma into the upper portion of the volcano. Seismic waves from low-frequency volcanic earthquake have large periods at all epicentral distances. Recordings of volcanic earthquakes from 2 to 4 April 1980 at sites 4 to 9 km from Mount St. Helens show two predominant periods of 0.55 and 1.0 sec. We speculate that seismic signals from the low-frequency volcanic earthquakes have a tectonic origin, but may be modified by pressure oscillations in nearby magma.

Overview of observed seismic signals on Mars

2020 ◽  
Author(s):  
Savas Ceylan ◽  
John F. Clinton ◽  
Domenico Giardini ◽  
Maren Böse ◽  
Martin van Driel ◽  
...  
Keyword(s):  
Energy Content ◽  
Low Frequency ◽  
Careful Analysis ◽  
Atmospheric Effects ◽  
Seismic Signals ◽  
S Wave ◽  
Ground Segment ◽  
Short Period ◽  
Data Content ◽  
Set Up

<p>InSight landed on Mars in late November 2018, and the SEIS package, which consists of one short period and one very broadband sensor, was deployed on the surface shortly after. The data returned by the InSight is monitored in a timely manner by the Marsquake Service (MQS), a ground segment support group of InSight that has been set up to establish and maintain the seismicity catalogue. The MQS has at least one member on duty who routinely checks the data for any type of seismic signals. All suspicious signals are then communicated to the InSight team after evaluation.</p><p>To date, MQS has identified more than 365 events which are classified into two general families as high and low frequency, with each family having unique features in terms of their energy content. The most distinct quakes detected so far belong to the low frequency family that occurred on Sol 173 and 235, and have clear P and S-wave arrivals that reveal a distance around 30 degrees east of the lander, pointing the region in the vicinity of Cerberus Fossae. In addition to the signals of seismic origin, the SEIS data contain features that originate from other sources such as atmospheric effects or electronics. Part of these non-seismic observations may resemble quakes which may lead to wrong interpretations, and therefore require careful analysis.</p><p>Here, we show examples of signals of both seismic and non-seismic origins. We describe the characteristics of these observations in time and frequency domains in order to give an overview of martian data content.</p>

Denoising of seismic signals based on empirical mode decomposition-wavelet thresholding

2020 ◽  
pp. 107754632092684
Author(s):  
Li Long ◽  
Xiulan Wen ◽  
Yixue Lin
Keyword(s):  
Empirical Mode Decomposition ◽  
Seismic Waves ◽  
Low Frequency ◽  
Wavelet Thresholding ◽  
Seismic Signals ◽  
Denoising Method ◽  
Intrusion Prevention ◽  
Mode Decomposition ◽  
Empirical Mode Decomposition Method ◽  
Feature Information

Unattended object detection systems have seen full applications in military surveillance, object recognition, and intrusion prevention. When applied to actual work scenarios, these systems have problems such as low recognition accuracy, low positioning accuracy, and weak detection effect of distant objects. Obtainment of enough feature information concerning the effective signals is critical to target recognition. This work focuses on interference in seismic signals and the way to store the feature information of effective signals. First, the authors analyzed the frequency and attenuation characteristics of seismic waves of typical target sites, in which the Rayleigh wave is suitable for the detection of the energy of seismic signals produced by human targets and vehicles. As seismic signals are low-frequency waves, the authors researched the performance of the empirical mode decomposition method and the wavelet thresholding method in denoising seismic signals, and an improved empirical mode decomposition-wavelet threshold denoising method is proposed. The test result shows that the improved denoising method can effectively remove noise in seismic signals and preserve the effective signals of the target.

scholarly journals Seismology of the Oso-Steelhead landslide

2014 ◽  
Vol 2 (12) ◽  
pp. 7309-7327 ◽  
Author(s):  
C. Hibert ◽  
C. P. Stark ◽  
G. Ekström
Keyword(s):  
Surface Waves ◽  
Slope Failure ◽  
Source Parameters ◽  
Seismic Energy ◽  
Seismic Signals ◽  
Period Analysis ◽  
Long Period ◽  
Landslide Volume ◽  
Short Period ◽  
Seismic Records

Abstract. We carry out a combined analysis of the short- and long-period seismic signals generated by the devastating Oso-Steelhead landslide that occurred on 22 March 2014. The seismic records show that the Oso-Steelhead landslide was not a single slope failure, but a succession of multiple failures distinguished by two major collapses that occurred approximately three minutes apart. The first generated long-period surface waves that were recorded at several proximal stations. We invert these long-period signals for the forces acting at the source, and obtain estimates of the first failure runout and kinematics, as well as its mass after calibration against the mass-center displacement estimated from remote-sensing imagery. Short-period analysis of both events suggests that the source dynamics of the second are more complex than the first. No distinct long-period surface waves were recorded for the second failure, which prevents inversion for its source parameters. However, by comparing the seismic energy of the short-period waves generated by both events we are able to estimate the volume of the second. Our analysis suggests that the volume of the second failure is about 15–30% of the total landslide volume, which is in agreement with ground observations.

scholarly journals On the characterization of seismic signals generated by snow avalanches for monitoring purposes

2001 ◽  
Vol 32 ◽  
pp. 268-274 ◽  
Author(s):  
E. Suriñach ◽  
G. Furdada ◽  
F. Sabot ◽  
B. Biesca ◽  
J. M. Vilaplana
Keyword(s):  
Seismic Waves ◽  
Seismic Energy ◽  
Time Lapse ◽  
Seismic Signals ◽  
Avalanche Size ◽  
Local Site ◽  
Video Images ◽  
Time Domains ◽  
Seismic Characterization

AbstractSeismic signals from artificially released avalanches were studied in an attempt to characterize them for avalanche-monitoring purposes. The seismic signals generated by different sizes and types of avalanches were recorded and analyzed in the time and frequency domains. Synchronized recordings of the corresponding seismic signals and the video images of the evolution of the avalanches were obtained together with a detailed cartography. Characteristic signatures in the frequency and time domains were found to depend on the characteristics of the avalanche path and measuring location, but to be mostly independent of avalanche size. The source of the different parts of the recorded seismic signals was determined. A relationship was observed between the avalanche size and the amplitude of the signals. Given the presence of local site effects, a prior seismic characterization of the avalanche path in relation to the recording sites is necessary for monitoring purposes. Moreover” it was found that sliding slabs in the early phase of acceleration produce little seismic energy, resulting in a time lapse between the observable start of the avalanche and the arrival of the detectable seismic waves at the receiving station.

Investigation of a method for determining stress accumulation at depth

1967 ◽  
Vol 57 (5) ◽  
pp. 891-911 ◽  
Author(s):  
Joseph D. Eisler
Keyword(s):  
Field Experiment ◽  
Seismic Waves ◽  
Seismic Energy ◽  
Laboratory Measurements ◽  
Initial Field ◽  
The Earth ◽  
Stressed Region ◽  
Compressional Velocity ◽  
Stress Accumulation ◽  
Better Than

abstract Measurement of stress accumulation at depth could serve as the basis for predicting earthquakes. Based on laboratory measurements of rock samples, stress accumulation in the earth can be estimated from changes in the compressional velocity of seismic waves traversing the stressed region, provided the travel times can be determined with precision. An initial field experiment performed in the Gabilan Range near Salinas, California, using 100-kilogram charges, demonstrated that seismic energy could be reliably detected up to 42 kilometers away, that the character of the recorded signal was closely repeatable for successive shots, and that the precision of timing was better than ±1 millisecond.

scholarly journals GEOPHONES IN LOCAL SEISMOLOGICAL NETWORKS

2019 ◽  
Vol 2 (3) ◽  
pp. 140-146
Author(s):  
Petr Dergach ◽  
Anton Duchkov ◽  
Vyacheslav Yushin
Keyword(s):  
Frequency Band ◽  
Low Frequency ◽  
Seismic Energy ◽  
Seismic Signals ◽  
Deconvolution Algorithm ◽  
Special Software ◽  
Method Of Assessment

In this paper, a method of assessment of geophones capability in seismological networks is described. The expansion of records frequency band, which are needed in this case, is performed by special software (low-frequency deconvolution algorithm). The main feature of the work is that the possibility of deconvolution is linked to the seismic energy of events, and not only to the level of the original seismic signals.

Geomorphologically-controlled seismic signals at Mount St. Helens volcano

2021 ◽  
Author(s):  
Luca De Siena ◽  
Simona Gabrielli ◽  
Matteo Spagnolo
Keyword(s):  
Morphological Difference ◽  
Low Frequency ◽  
Primary Source ◽  
Seismic Signals ◽  
S Waves ◽  
Seismic Waveforms ◽  
The North ◽  
Buried Fault ◽  
Geomorphological Features ◽  
Mount St Helens

<p>In volcanoes, topography and shallow morphology can substantially modify seismic signals, tracing anisotropic signatures in the crust's most surficial layers. To better understand the influence of key morphologies, forward modelling of the seismic waveforms is fundamental.  Here, we introduce a forward model of the seismic wave equation developed with finite-differences schemes in anisotropic viscoelastic media. The observation of geomorphological features and the surficial geology map of Mount St. Helens are used to reproduce the scattering and anisotropic effects caused by shallow heterogeneity on seismic signals. The main aim is to understand if and to which lengths lateral anisotropic variations in geomorphological features control the generation and propagation of low-frequency seismic signals, focusing especially on the timing of surface-wave enhancement.</p><p>The model shows how the geomorphology-derived anisotropy controls the travel times of the horizontally polarized S waves (SH), in particular along with two directions: WNW-ESE, following the trend of a buried fault, and NS, consistent with the main morphological difference between southern (mostly untouched by the 1980 eruption) and northern (collapsed in 1980’s blast) flanks of the volcano. An analysis of the waveforms of a shallow event of 2005 (during the last eruption of Mt. St. Helens), located in the crater, shows how an isotropic model can reproduce the arrival of the SH wave at high frequencies (10 Hz). The introduction of an effective anisotropic medium is necessary to explain the arrivals for stations deployed across the north-northwestern flank of the volcano at lower frequencies (1 Hz and 6 Hz). The heterogeneity in the crater (e.g., the glacier inside the crater covered by a rock-debris layer) can create interfaces made mostly of unconsolidated materials. As also demonstrated by radiative transfer simulation, the crater acts as a primary source of surface waves dominating the seismic signals.</p>

Statistical analysis of irregular wave-guide influences on regional seismic discriminants in China: Additional results for Pn/Sn, Pn/Lg, and Pg/Sn

1998 ◽  
Vol 88 (6) ◽  
pp. 1504-1510
Author(s):  
Guangwei Fan ◽  
Thorne Lay
Keyword(s):  
Crustal Structure ◽  
Seismic Waves ◽  
Low Frequency ◽  
Multivariate Regression Analysis ◽  
Crustal Thickness ◽  
Western China ◽  
The Tibetan Plateau ◽  
Sediment Thickness ◽  
Amplitude Ratios ◽  
Short Period

Abstract Reducing scatter in measurements of regional-phase amplitude ratios is desirable for seismic discrimination applications and also provides insight into crustal structure controls on energy partitioning of regional seismic waves. Our previous analysis (Fan and Lay, 1998) of the regional seismic discriminant, Pg/Lg, indicated that variations in crustal structure cause path-specific fluctuations of those amplitude ratios for earthquakes recorded at broadband station WMQ in western China. In this study, we extend our multivariate regression analysis to Pn/Sn, Pn/Lg, and Pg/Sn amplitude ratios recorded at WMQ in frequency bands of 0.75 to 1.5 Hz, 1.5 to 3.0 Hz, and 3.0 to 6.0 Hz for the suite of path-specific parameters: path length, mean path elevation, variance of topography along the path, rms topographic slope variations, mean crustal thickness, and mean sediment thickness. Optimal three- and four-parameter models all achieve reductions in variance of the measurements relative to conventional distance corrections. At low frequency, the improvements for ratios involving Pg can be more than a factor of 2. For all short-period amplitude ratios, mean path elevation seems to play an important role. While crustal thickness and sediment thickness affect ratios involving Pg, topographic variance and surface slope variations have more influence on ratios involving Pn. Strong crustal variations associated with the structure of the Tibetan Plateau are responsible for much of the amplitude variations.

SEISMIC WAVE PROPAGATION

Geophysics ◽  
1950 ◽  
Vol 15 (1) ◽  
pp. 50-60 ◽  
Author(s):  
D. H. Clewell ◽  
R. F. Simon
Keyword(s):  
High Frequency ◽  
Seismic Waves ◽  
Low Frequency ◽  
Seismic Energy ◽  
Seismic Wave Propagation ◽  
Frequency Range ◽  
Energy Propagation ◽  
Scattered Energy ◽  
Solid Friction ◽  
Theoretical Considerations

Speculations are made regarding the significance of the well‐known observation that seismic reflection energy is usually in the frequency range of from 20 to 100 cycles per second. The general absence of reflected energy below 20 cps is attributed to the fact that the wavelengths of seismic waves in this frequency range are becoming large compared to the thicknesses of reflecting beds; accordingly, the reflection coefficients are low with the results that the geologic section appears more or less homogeneous, the low frequency energy is unweakened by reflections, is transmitted efficiently, and can only return to the surface by refraction. As the frequency is increased the wavelengths become comparable to the vertical discontinuities represented by stratification and more efficient reflection takes place with the result that reflected energy is returned and detected at the surface. At still higher frequencies the wavelengths become comparable to small inhomogeneities distributed at random throughout the geologic section and the energy is therefore diffused and scattered to such an extent that transmission into the earth is limited. This weakening of the main wave front by scattering, plus the weakening by absorption processes involving viscous and solid friction, constitute an effective cutting off of high frequency transmission. The high frequency scattered energy diffuses back to the surface and appears on the seismogram as “hash,” unless eliminated by filters, or is absorbed before it reaches the surface. Such a speculative picture of seismic energy propagation accounts qualitatively for (1) the continuous reception of random energy that is always superimposed upon the reflection energy, (2) the tendency for deep reflections to be of lower frequency than shallow reflections, and (3) the fact that theoretical considerations of absorption do not always account for known attenuation of high frequency seismic energy.

Frequency Response Analysis of Piecewise Nonlinear Vibration Isolator

2005 ◽  
Author(s):  
Patrick Stahl ◽  
G. Nakhaie Jazar
Keyword(s):  
Low Frequency ◽  
High Amplitude ◽  
Relative Displacement ◽  
Response Analysis ◽  
Frequency Response Analysis ◽  
State Behavior ◽  
Vibration Isolators ◽  
Short Period ◽  
Secondary Suspension ◽  
Low Amplitude

Non-smooth piecewise functional isolators are smart passive vibration isolators that can provide effective isolation for high frequency/low amplitude excitation by introducing a soft primary suspension, and by preventing a high relative displacement in low frequency/high amplitude excitation by introducing a relatively damped secondary suspension. In this investigation a linear secondary suspension is attached to a nonlinear primary suspension. The primary is assumed to be nonlinear to model the inherent nonlinearities involved in real suspensions. However, the secondary suspension comes into action only during a short period of time, and in mall domain around resonance. Therefore, a linear assumption for the secondary suspension is reasonable. The dynamic behavior of the system subject to a harmonic base excitation has been analyzed utilizing the analytic results derived by applying the averaging method. The analytic results match very well in the transition between the two suspensions. A sensitivity analysis has shown the effect of varying dynamic parameters in the steady state behavior of the system.

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