Rupture Process of the M 7.9 Denali Fault, Alaska, Earthquake: Subevents, Directivity, and Scaling of High-Frequency Ground Motions

2004 ◽  
Vol 94 (6B) ◽  
pp. S234-S255 ◽  
Author(s):  
A. Frankel
Keyword(s):  
High Frequency ◽  
Ground Motions ◽  
Rupture Process ◽  
Denali Fault ◽  
Alaska Earthquake

Landslides Triggered by the 2002 Denali Fault, Alaska, Earthquake and the Inferred Nature of the Strong Shaking

2004 ◽  
Vol 20 (3) ◽  
pp. 669-691 ◽  
Author(s):  
Randall W. Jibson ◽  
Edwin L. Harp ◽  
William Schulz ◽  
David K. Keefer
Keyword(s):  
High Frequency ◽  
Near Field ◽  
Rupture Zone ◽  
Fault Rupture ◽  
Rock Falls ◽  
Ground Shaking ◽  
Denali Fault ◽  
Rock Avalanches ◽  
Landslide Distribution ◽  
Alaska Earthquake

The 2002 M7.9 Denali fault, Alaska, earthquake triggered thousands of landslides, primarily rock falls and rock slides, that ranged in volume from rock falls of a few cubic meters to rock avalanches having volumes as great as 15×106m3. The pattern of landsliding was unusual; the number of slides was less than expected for an earthquake of this magnitude, and the landslides were concentrated in a narrow zone 30-km wide that straddled the fault rupture over its entire 300-km length. The large rock avalanches all clustered along the western third of the rupture zone where acceleration levels and ground-shaking frequencies are thought to have been the highest. Inferences about near-field strong shaking characteristics drawn from the interpretation of the landslide distribution are consistent with results of recent inversion modeling that indicate high-frequency energy generation was greatest in the western part of the fault rupture zone and decreased markedly to the east.

Calibration of a Semi-Stochastic Procedure for Simulating High-Frequency Ground Motions

2013 ◽  
Vol 29 (4) ◽  
pp. 1495-1519 ◽  
Author(s):  
Emel Seyhan ◽  
Jonathan P. Stewart ◽  
Robert W. Graves
Keyword(s):  
High Frequency ◽  
Ground Motions ◽  
Random Phase ◽  
Low Frequencies ◽  
Intensity Measures ◽  
Amplitude Spectra ◽  
Random Site ◽  
Broadband Ground Motion Simulation ◽  
Broadband Ground Motion ◽  
Attenuation Bias

Broadband ground motion simulation procedures typically utilize physics-based modeling at low frequencies, coupled with semi-stochastic procedures at high frequencies. The high-frequency procedure considered here combines deterministic Fourier amplitude spectra (dependent on source, path, and site models) with random phase. Previous work showed that high-frequency intensity measures from this simulation methodology attenuate faster with distance and have lower intra-event dispersion than in empirical equations. We address these issues by increasing crustal damping (Q) to reduce distance attenuation bias and by introducing random site-to-site variations to Fourier amplitudes using a lognormal standard deviation ranging from 0.45 for Mw < 7 to zero for Mw 8. Ground motions simulated with the updated parameterization exhibit significantly reduced distance attenuation bias and revised dispersion terms are more compatible with those from empirical models but remain lower at large distances (e.g., > 100 km).

Numerical Modeling of Near Fault Seismic Ground Motion for Denali Fault

2021 ◽  
Vol 12 (2) ◽  
pp. 0-0
Keyword(s):  
Ground Motion ◽  
Peak Ground Acceleration ◽  
Numerical Study ◽  
Ground Motions ◽  
Numerical Results ◽  
Fault Rupture ◽  
Ground Acceleration ◽  
Denali Fault ◽  
Near Fault ◽  
Good Agreement

An effective earthquake (Mw 7.9) struck Alaska on 3 November, 2002. This earthquake ruptured 340 km along Susitna Glacier, Denali and Totschunda faults in central Alaska. The peak ground acceleration (PGA) was recorded about 0.32 g at station PS10, which was located 3 km from the fault rupture. The PGA would have recorded a high value, if more instruments had been installed in the region. A numerical study has been conducted to find out the possible ground motion record that could occur at maximum horizontal slip during the Denali earthquake. The current study overcomes the limitation of number of elements to model the Denali fault. These numerical results are compared with observed ground motions. It is observed that the ground motions obtained through numerical analysis are in good agreement with observed ground motions. From numerical results, it is observed that the possible expected PGA is 0.62 g at maximum horizontal slip of Denali fault.

Rupture Process of the Mainshock of the 2019 Ridgecrest Earthquake Sequence from Waveform Inversion with Empirical Green’s Functions

2021 ◽  
Author(s):  
Shuang-Lan Wu ◽  
Atsushi Nozu ◽  
Yosuke Nagasaka
Keyword(s):  
Green's Functions ◽  
Green’S Functions ◽  
Ground Motions ◽  
Strong Motion ◽  
Rupture Process ◽  
Earthquake Sequence ◽  
Slip Model ◽  
Near Fault ◽  
Empirical Green’S Functions ◽  
Empirical Green's Functions

ABSTRACT The 2019 Mw 7.1 mainshock of the Ridgecrest earthquake sequence, which was the first event exceeding Mw 7.0 in California since the 1999 Hector Mine earthquake, caused near-fault ground motions exceeding 0.5g and 70  cm/s. In this study, the rupture process and the generation mechanism of strong ground motions of the mainshock were investigated through waveform inversions of strong-motion data in the frequency range of 0.2–2.0 Hz using empirical Green’s functions (EGFs). The results suggest that the mainshock involved two large slip regions: the primary one with a maximum slip of approximately 4.4 m was centered ∼3  km northwest of the hypocenter, which was slightly shallower than the hypocenter, and the secondary one was centered ∼25  km southeast of the hypocenter. Outside these regions, the slip was rather small and restricted to deeper parts of the fault. A relatively small rupture velocity of 2.1  km/s was identified. The robustness of the slip model was examined by conducting additional inversion analyses with different combinations of EGF events and near-fault stations. In addition, using the preferred slip model, we synthesized strong motions at stations that were not used in the inversion analyses. The synthetic waveforms captured the timing of the main phases of observed waveforms, indicating the validity of the major spatiotemporal characteristics of the slip model. Our large slip regions are also generally visible in the models proposed by other researchers based on different datasets and focusing on lower frequency ranges (generally lower than 0.5 Hz). In particular, two large slip regions in our model are very consistent with two of the four subevents identified by Ross et al. (2019), which may indicate that part of the large slip regions that generated low-frequency ground motions also generated high-frequency ground motions up to 2.0 Hz during the Ridgecrest mainshock.

scholarly journals Capturing Regional Variations of Hard‐Rock Attenuation in Europe

2019 ◽  
Vol 109 (4) ◽  
pp. 1401-1418 ◽  
Author(s):  
Marco Pilz ◽  
Fabrice Cotton ◽  
Riccardo Zaccarelli ◽  
Dino Bindi
Keyword(s):  
High Frequency ◽  
Hard Rock ◽  
Epistemic Uncertainty ◽  
Ground Motions ◽  
Soft Soil ◽  
Coda Waves ◽  
Corner Frequency ◽  
S Wave ◽  
Empirical Parameter ◽  
Regional Variations

Abstract A proper assessment of seismic reference site conditions has important applications as they represent the basis on which ground motions and amplifications are generally computed. Besides accounting for the average S‐wave velocity over the uppermost 30 m (VS30), the parameterization of high‐frequency ground motions beyond source‐corner frequency received significant attention. κ, an empirical parameter introduced by Anderson and Hough (1984), is often used to represent the spectral decay of the acceleration spectrum at high frequencies. The lack of hard‐rock records and the poor understanding of the physics of κ introduced significant epistemic uncertainty in the final seismic hazard of recent projects. Thus, determining precise and accurate regional hard‐rock κ0 values is critical. We propose an alternative procedure for capturing the reference κ0 on regional scales by linking the well‐known high‐frequency attenuation parameter κ and the properties of multiple‐scattered coda waves. Using geological and geophysical data around more than 1300 stations for separating reference and soft soil sites and based on more than 10,000 crustal earthquake recordings, we observe that κ0 from multiple‐scattered coda waves seems to be independent of the soil type but correlated with the hard‐rock κ0, showing significant regional variations across Europe. The values range between 0.004 s for northern Europe and 0.020 s for the southern and southeastern parts. On the other hand, measuring κ (and correspondingly κ0) on the S‐wave window (as classically proposed), the results are strongly affected by transmitted (reflected, refracted, and scattered) waves included in the analyzed window biasing the proper assessment of κ0. This effect is more pronounced for soft soil sites. In this way, κ0coda can serve as a proxy for the regional hard‐rock κ0 at the reference sites.

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