Attenuation of short period seismic waves at Etna as compared to other volcanic areas

abstract A magnitude (ML) scaling law has been derived from the strong-motion data base of the San Fernando earthquake of February 9, 1971, and the results have been compared with other strong-motion recordings obtained from 62 earthquakes in the Western United States. The relationship derived is ML = 3.21 + 1.35 log10Δ + log10v. An excellent agreement was obtained between the determined ML values in this study and those evaluated by Kanamori and Jennings (1978). This scaling law is applicable to the collected data from 63 earthquakes whose local magnitudes range from about 4.0 to 7.2, recorded at epicentral distances between about 5 to 300 km, and with short-period seismic waves in the range of 0.2 to 3.0 sec. The Long Beach earthquake of 1933, with an ML = 6.3 (PAS) and an ML = 6.43 ± 0.36 as determined by Kanamori and Jennings is in agreement with an ML = 6.49 ± 0.32 obtained in this study. The Imperial Valley earthquake of 1940, with an ML = 6.5 (PAS), compares well with an ML = 6.5 as determined in this study. The Kern County earthquake of 1952, with an ML = 7.2 (BRK), is in fairly good agreement with the ML = 7.0 ± 0.2 obtained in this investigation. This value is significantly lower than the commonly quoted 7.7 value for this event. The San Francisco earthquake of 1957, with an ML = 5.3 (BRK), agrees very well with an ML = 5.3 ± 0.1 as determined in this study. The Parkfield earthquake of 1966 has an ML = 5.8 ± 0.3, which is consistent with the 5.6 (PAS). The procedure developed here is applied to the data base obtained from the Western United States strong-motion recordings. The procedure allows the evaluation of ML for moderate and larger earthquakes from the first integration of the strong-motion accelerograms and allows the direct determination of ML from the scaled amplitudes in a rapid, economical, and accurate manner. It also has allowed for the extension of the trend of the attenuation curve for horizontal particle velocities at distances less than 5 km for different size events.

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Seismic response analysis of loess site under far-field bedrock ground motion of the Wenchuan earthquake

PLoS ONE ◽

10.1371/journal.pone.0254871 ◽

2021 ◽

Vol 16 (7) ◽

pp. e0254871

Author(s):

Tuo Chen

Keyword(s):

Ground Motion ◽

Seismic Waves ◽

Linear Method ◽

Soil Layer ◽

Resonance Phenomenon ◽

Amplification Coefficient ◽

Response Analysis ◽

Topographic Effects ◽

Far Field ◽

Short Period

In this paper, considering the far-field seismic input, an accelerogram recorded in the bedrock at Wuquan Mountain in Lanzhou city during the 2008 Wenchuan Ms8.0 earthquake was selected, and numerical dynamic analyses were conducted. The one-dimensional equivalent linear method was implemented to estimate the ground motion effects in the loess regions. Thereafter, slope topographic effects on ground motion were studied by applying the dynamic finite-element method. The results revealed the relationship between the PGA amplification coefficients and the soil layer thickness, which confirmed that the dynamic response of the sites had obvious nonlinear characteristics. The results also showed that there was an obvious difference in the dynamic magnification factor between the short-period and long-period structures. Moreover, it was found that the amplification coefficient of the observation point at the free surface was greater than the point inside the soil at the same depth, which mainly occurred in the upper slope. Through this study, the quantitative assessment of ground motion effects in loess regions can be approximately estimated, and the amplification mechanism of the far-field ground motion mechanism can be further explained. In addition to the refraction and reflection theory of seismic waves, the resonance phenomenon may help explain the slope topographic effect through spectrum analysis.

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Application of BRFP New-Type Anchor Cable Material in High Slopes against Earthquakes

Advances in Civil Engineering ◽

10.1155/2021/6689718 ◽

2021 ◽

Vol 2021 ◽

pp. 1-19

Author(s):

Honggang Wu ◽

Zhixin Wu ◽

Hao Lei ◽

Tianwen Lai

Keyword(s):

Dynamic Response ◽

Seismic Wave ◽

Seismic Waves ◽

Response Spectrum ◽

Basalt Fiber ◽

Shaking Table ◽

Measuring Point ◽

Reinforced Plastics ◽

Short Period ◽

The Impact

To clarify the feasibility of BFRP (basalt fiber reinforced plastics) anchors instead of steel anchors in the seismic application of slopes under different vibration strengths, a series of shaking table tests were carried out to strengthen the slope using BFRP anchors and steel anchors, respectively. By studying the dynamic response recorded in the slope model and the observed experimental phenomena, the acceleration dynamic response and displacement spectrum dynamic response of the two slope models were analyzed. The test results show that the deformation stage of the slope reinforced by the two types of anchors is basically the same during the test, that is, elastic, plastic (potential sliding surface and plastic strengthening), and failure stages, respectively. The slope is in the elastic stage before the 0.2 g seismic wave, and it gradually enters the plastic stage after the 0.4 g seismic wave. However, the peak acceleration and displacement of the slope reinforced by steel anchors are greater than those of the slope reinforced by BFRP anchors under the same working conditions of seismic waves. In addition, we found that the acceleration response spectrum distribution curve of each measuring point in the short period has an obvious amplification effect along the elevation, and its predominant period has a forward migration phenomenon with the increase of the height of the measuring point, which also indicates that the higher frequency seismic wave has a greater impact on the top of the slope. The BFRP anchors, as a kind of flexible structure supporting slope, can effectively reduce the impact of seismic waves on the slope and attenuate seismic waves to a certain extent compared with steel anchors. Furthermore, the BFRP anchors can be deformed in coordination with the slope, which can improve the overall working performance of the slope, especially limit the dynamic response of the middle and lower slopes. These results can provide a theoretical guide for the seismic design of BFRP anchors for high slopes.

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Attenuation of long period multiple using F-k filter and surface-related multiple elimination methods on 2D broadband seismic data from Morowali Waters, Sulawesi

IOP Conference Series Earth and Environmental Science ◽

10.1088/1755-1315/944/1/012005 ◽

2021 ◽

Vol 944 (1) ◽

pp. 012005

Author(s):

G L Situmeang ◽

H M Manik ◽

T B Nainggolan ◽

Susilohadi

Keyword(s):

Seismic Data ◽

Seismic Waves ◽

Frequency Bandwidth ◽

Long Period ◽

Time Migration ◽

Predictive Deconvolution ◽

Short Period ◽

Wide Range ◽

Marine Seismic ◽

Multiple Elimination

Abstract Wide range frequency bandwidth on seismic data is a necessity due to its close relation to resolution and depth of target. High-frequency seismic waves provide high-resolution imaging that defines thin bed layers in shallow sediment, while low-frequency seismic waves can penetrate into deeper target depth. As a result of broadband seismic technology, its wide range of frequency bandwidth is a suitable geophysical exploration method in the oil and gas industry. A major obstacle that is frequently found in marine seismic data acquisition is the existence of multiples. Short period multiple and reverberation are commonly attenuated by the predictive deconvolution method on prestack data. Advanced methods are needed to suppress long period multiple in marine seismic data. The 2D broadband marine seismic data from deep Morowali Waters, Sulawesi, contains both short and long period multiples. The predictive deconvolution, which is applied to the processing sequences, successfully eliminates short period multiple on prestack data. The combination of F-k filter and Surface Related Multiple Elimination (SRME) methods are successful in attenuating long period multiple of the 2D broadband marine seismic data. The Prestack Time Migration section shows fine resolution of seismic images.

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Slow earthquake signatures in the ratio between acoustic and internal gravity wave amplitudes in coseismic ionospheric disturbances

10.5194/egusphere-egu21-758 ◽

2021 ◽

Author(s):

Kosuke Heki ◽

Yuki Takasaka

Keyword(s):

Gravity Wave ◽

Seismic Waves ◽

Internal Gravity Wave ◽

Electron Content ◽

Ionospheric Disturbances ◽

Atmospheric Waves ◽

Crustal Movements ◽

Long Period ◽

Short Period ◽

Vertical Crustal Movements

<p>Frequency spectra of seismic waves from a fault rupture reflects the size of the faults, i.e. relatively large amplitudes of long period waves are excited by larger earthquakes. Anomalies in rise times of the fault movements would also influence the spectra. For example, earthquakes characterized by slow faulting, known as tsunami earthquakes, excite large tsunamis for the amplitudes of short-period seismic waves. In this study, we compare amplitudes of long- and short-period atmospheric waves excited by vertical crustal movements associated with earthquake faulting. Such atmospheric waves often reach the ionospheric F region and cause coseismic ionospheric disturbances (CID) observed as oscillations in ionospheric total electron content (TEC), with ground Global Navigation Satellite System (GNSS) receivers. CID often includes long-period internal gravity wave (IGW) components in addition to short period acoustic wave (AW) components. The latter has a period of ~4 minutes and propagate by 0.8-1.0 km/s, while the former has a period of ~12 minutes and propagate as fast as 0.2-0.3 km/s. Here we compare amplitudes of these two different waves for five earthquakes, 2011 Tohoku-oki (Mw9.0), 2010 Maule (Mw8.8), 1994 Hokkaido-Toho-Oki (Mw8.3), 2003 Tokachi-oki (Mw8.0), and the 2010 Mentawai (Mw7.9) earthquakes, using data from regional dense GNSS networks. We found two important features, i.e. (1) larger earthquakes show larger IGW/AW amplitude ratios, and (2) Mentawai earthquake, a typical tsunami earthquake, exhibits abnormally large IGW amplitudes relative to AW amplitudes. These findings demonstrate that earthquakes with longer durations for faulting, or with longer times for vertical crustal movements, excite longer period atmospheric waves such as IGW more efficiently.</p>

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

Bulletin of the Seismological Society of America ◽

10.1785/bssa07306a1797 ◽

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.

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