Simulating strong motions of large earthquakes using recordings of small earthquakes: the Loma Prieta mainshock as a test case

1995 ◽  
Vol 85 (4) ◽  
pp. 1144-1160
Author(s):  
Arthur Frankel
Keyword(s):  
Stress Drop ◽  
Site Response ◽  
Strong Motion ◽  
Site Effect ◽  
Corner Frequency ◽  
Simple Method ◽  
Strong Motion Records ◽  
Loma Prieta Earthquake ◽  
Loma Prieta ◽  
Large Earthquakes

Abstract A simple method is developed for predicting ground motions for future large earthquakes for specific sites by summing and filtering recordings of adjacent small earthquakes. This method is tested by simulating strong-motion records for the Loma Prieta earthquake (M 7.0) using aftershocks (M 3.7 to 4.0) recorded at the same sites. I use an asperity rupture model where the rms stress drop averaged over the fault plane is constant with moment. The observed spectra indicate that stress drop remains constant from the M 3 aftershocks up to the M 7 mainshock, about six orders of magnitude in seismic moment. Each simulation sums the seismogram of one aftershock with time delays appropriate for propagating rupture and incorporates directivity and site response. The simulation scales the spectrum in accordance with a constant stress drop, ω−2 source model. In this procedure, the high-frequency energy of the aftershock sum above the corner frequency of the aftershock is not reduced when it is convolved with the mainshock slip velocity function, unlike most previous methods of summation. For most cases, the spectra (0.6 to 20 Hz), peak accelerations, and durations of the simulated mainshock records are in good agreement with the observed strong-motion records, even though only one aftershock waveform was used in each simulation. This agreement indicates that the response of these soil sites is essentially linear for accelerations up to about 0.3 g. The summed aftershock records display the same site-dependent values of fmax as the mainshock records, implying that fmax is a site effect rather than a property of the mainshock rupture process.

Strong-Motion Records at Army Hospitals in California from the Loma Prieta Earthquake of 17 October 1989

1990 ◽  
Author(s):  
Pamalee A. Brady ◽  
James B. Gambill ◽  
William J. Gordon ◽  
John R. Hayes ◽  
Jr
Keyword(s):  
Strong Motion ◽  
Strong Motion Records ◽  
Loma Prieta Earthquake ◽  
Army Hospitals ◽  
Loma Prieta

The accuracy of soil response estimates using soil-to-rock spectral ratios

1996 ◽  
Vol 86 (2) ◽  
pp. 519-523
Author(s):  
Igor A. Beresnev ◽  
Kuo-Liang Wen
Keyword(s):  
Site Response ◽  
Soft Soil ◽  
Strong Motion ◽  
Finite Depth ◽  
Spectral Ratios ◽  
Site Specific ◽  
Soil Response ◽  
Strong Motion Records ◽  
The Real ◽  
Specific Amplification

Abstract Spectral ratios between soft soil and reference rock sites are often used to predict the sedimentary site response to earthquakes. However, their relationship with the genuine site-specific amplification function is often unclear. We compare the soil-to-rock spectral ratios between the stations that are 3.3 km apart with the “genuine” response given by the ratios between the surface and 17 and 47 m downhole. Data from the SMART1 array in Taiwan are used. The “weak” and “strong” motion records are addressed separately to allow for nonlinear soil response. The soil-to-rock spectral ratios are nearly identical to the “true” amplification at the frequencies from 1 to 10 Hz, if the finite depth of the borehole is taken into account. They correctly capture the strong-motion deamplification effect. However, the soil-to-rock spectral ratios are roughly 1.4 times more uncertain than surface-to-47-m ratios. In summary, the soil-to-rock spectral ratios can be considered as the reliable estimates of the real site response.

scholarly journals Analysis of strong-motion data of the 1990 Eastern Sicily earthquake

1995 ◽  
Vol 38 (2) ◽  
Author(s):  
M. Di Bona ◽  
M. Cocco ◽  
A. Rovelli ◽  
R. Berardi ◽  
E. Boschi
Keyword(s):  
Frequency Band ◽  
Stress Drop ◽  
Seismic Moment ◽  
Ground Motions ◽  
Broad Band ◽  
Strong Motion ◽  
Moment Magnitude ◽  
Corner Frequency ◽  
Local Magnitude ◽  
The Moment

The strong motion accelerograms recorded during the 1990 Eastern Sicily earthquake have been analyzed to investigate source and attenuation parameters. Peak ground motions (peak acceleration, velocity and displacement) overestimate the values predicted by the empirical scaling law proposed for other Italian earthquakes, suggesting that local site response and propagation path effects play an important role in interpreting the observed time histories. The local magnitude, computed from the strong motion accelerograms by synthesizing the Wood-Anderson response, is ML = 5.9, that is sensibly larger than the local magnitude estimated at regional distances from broad-band seismograms (ML = 5.4). The standard omega-square source spectral model seems to be inadequate to describe the observed spectra over the entire frequency band from 0.2 to 20 Hz. The seismic moment estimated from the strong motion accelerogram recorded at the closest rock site (Sortino) is Mo = 0.8 x 1024 dyne.cm, that is roughly 4.5 times lower than the value estimated at regional distances (Mo = 3.7 x 1024 dyne.cm) from broad-band seismograms. The corner frequency estimated from the accelera- tion spectra i.5 J; = 1.3 Hz, that is close to the inverse of the dUl.ation of displacement pulses at the two closest recording sites. This value of corner tì.equency and the two values of seismic moment yield a Brune stress drop larger than 500 bars. However, a corner frequency value off; = 0.6 Hz and the seismic moment resulting from regional data allows the acceleration spectra to be reproduced on the entire available frequency band yielding to a Brune stress drop of 210 bars. The ambiguity on the corner frequency value associated to this earthquake is due to the limited frequency bandwidth available on the strong motion recordil1gs. Assuming the seismic moment estimated at regional distances from broad-band data, the moment magnitude for this earthquake is 5.7. The higher local magnitude (5.9) compared with the moment magnitude (5.7) is due to the weak regional attenuation. Beside this, site amplifications due to surface geology have produced the highest peak ground motions among those observed at the strong motion sites.

Source parameter analysis from strong motion records of the Friuli, Italy, earthquake sequence (1976-1977)

1987 ◽  
Vol 77 (4) ◽  
pp. 1127-1146
Author(s):  
Giuseppe De Natale ◽  
Raul Madariaga ◽  
Roberto Scarpa ◽  
Aldo Zollo
Keyword(s):  
Frequency Domain ◽  
Stress Drop ◽  
High Frequency ◽  
Epicentral Distance ◽  
Strong Motion ◽  
Source Model ◽  
Parameter Analysis ◽  
Corner Frequency ◽  
Spectral Parameters ◽  
Single Station

Abstract Time and frequency domain analyses are applied to strong motion data recorded in Friuli, Italy, during 1976 to 1977. An inversion procedure to estimate spectral parameters (low frequency level, corner frequency, and high frequency decay) has been applied to displacement spectra using a simple earthquake source model with a single corner frequency. The data were digitized accelerograms from ENEA-ENEL portable and permanent networks. Instrument-corrected SH waves were selected from a set of 138 three-component, hand-digitized records and 28 automatically digitized records. Thirty-eight events with stations having 8 to 32 km epicentral distance were studied. Different stress drop estimates were performed showing high values (200 to 300 bars, on the average) with seismic moments ranging from 2.8 × 1022 to 8.0 × 1024 dyne-cm. The observation of systematic higher values of Brune stress drop (obtained from corner frequencies) with respect to other time and frequency domain estimates of stress release, and the evidence on time series of multiple rupture episodes suggest that the observed corner frequencies are most probably related to subevent ruptures rather than the overall fault size. Seven events recorded at more than one station show a good correlation between rms, Brune, and dynamic stress drops, and a constant scaling of this parameter as a function of the seismic moment. When single station events are also considered, a slight moment dependence of these three stress drop estimates is observed differently. This may be explained by an inadequacy of the ω−2 high-frequency decay of the source model or by high-frequency attenuation due to propagation effects. The high-frequency cutoff of acceleration spectra indicates the presence of an Fmax in the range of 5 to 14 Hz, except for the stations where local site effects produce spectral peaks.

scholarly journals Rupture model of the 1989 Loma Prieta earthquake from the inversion of strong-motion and broadband teleseismic data

1991 ◽  
Vol 81 (5) ◽  
pp. 1540-1572 ◽  
Author(s):  
David J. Wald ◽  
Donald V. Helmberger ◽  
Thomas H. Heaton
Keyword(s):  
Ground Motion ◽  
Ground Motions ◽  
Strong Motion ◽  
High Gain ◽  
Temporal And Spatial Distribution ◽  
Origin Time ◽  
Loma Prieta Earthquake ◽  
Motion Data ◽  
Teleseismic Data ◽  
Loma Prieta

Abstract We have used 24 broadband teleseismic and 48 components of local strong-motion velocity records of the 1989 Loma Prieta earthquake in a formal inversion to determine the temporal and spatial distribution of slip. Separate inversions of the teleseismic data (periods of 3 to 30 sec) or strong-motion data (periods of 1 to 5 sec) result in similar models. The data require bilateral rupture with relatively little slip in the region directly updip from the hypocenter. Slip is concentrated in two patches: one centered 6 km northwest of the hypocenter at a depth of 12 km and with a maximum slip of 350 cm, and the other centered about 5 km southeast of the hypocenter at a depth of 16 km and with a maximum slip of 460 cm. The bilateral nature of the rupture results in large amplitude ground motions at sites located along the fault strike, both to the northwest and the southeast. However, the northwestern patch has a larger moment and overall stress drop and is, consequently, the source of the largest ground motion velocities, consistent with the observed recordings. This bilateral rupture also produces relatively modest ground motion amplitudes directly updip from the hypocenter, which is in agreement with the velocity ground motions observed at Corralitos. There is clear evidence of a foreshock (magnitude between 3.5 and 5.0) or a slow rupture nucleation about 2 sec before the main part of the rupture; the origin time implied by strong-motion trigger times is systematically 2 sec later than the time predicted from the high-gain regional network data. The seismic moment obtained from either of the separate data sets or both sets combined is about 3.0 × 1026 dyne-cm and the potency is 0.95 km3.

scholarly journals SITE RESPONSE AND SEISMIC WAVEFIELD IN TOLUCA CITY, MEXICO, FROM STRONG MOTION RECORDS

2006 ◽  
pp. 83
Author(s):  
Hugo Ferrer-Toledo ◽  
Martín Cárdenas-Soto ◽  
Francisco J. Chávez-García
Keyword(s):  
Site Response ◽  
Strong Motion ◽  
Strong Motion Records ◽  
Seismic Wavefield

The Loma Prieta earthquake, ground motion, and damage in Oakland, Treasure Island, and San Francisco

1991 ◽  
Vol 81 (5) ◽  
pp. 2019-2047
Author(s):  
Thomas C. Hanks ◽  
A. Gerald Brady
Keyword(s):  
Ground Motion ◽  
San Francisco ◽  
Strong Ground Motion ◽  
Strong Motion ◽  
Earthquake Ground Motion ◽  
Transverse Motion ◽  
Loma Prieta Earthquake ◽  
Loma Prieta ◽  
Treasure Island ◽  
Strong Ground

Abstract The basis of this study is the acceleration, velocity, and displacement wave-forms of the Loma Prieta earthquake (18 October 1989; M = 7.0) at two rock sites in San Francisco, a rock site on Yerba Buena Island, an artificial-fill site on Treasure Island, and three sites in Oakland underlain by thick sections of poorly consolidated Pleistocene sediments. The waveforms at the three rock sites display a strong coherence, as do the three sedimentary sites in Oakland. The duration of strong motion at the rock sites is very brief, suggestive of an unusually short source duration for an earthquake of this size, while the records in Oakland show strong amplification effects due to site geology. The S-wave group at Treasure Island is phase coherent with the Oakland records, but at somewhat diminished amplitudes, until the steps in acceleration at approximately 15 sec, apparently signaling the onset of liquefaction. All seven records clearly show shear-wave first motion opposite to that expected for the mainshock radiation pattern and peak amplitudes greater than expected for sites at these distances (95 ± 3 km) from an earthquake of this magnitude. While the association between these ground motion records and related damage patterns in nearby areas has been easily and eagerly accepted by seismological and engineering observers of them, we have had some difficulty in making such relationships quantitative or even just clear. The three Oakland records, from sites that form a nearly equilateral triangle about the Cypress Street viaduct collapse, are dominated by a long-period resonance (≃ 1 1/2-sec period) far removed from the natural frequency of the structure to transverse motion (2.5 Hz) or from high-frequency amplification bands observed in aftershock studies. A spectral ratio arbiter of this discrepancy confuses it further. The failure of the East Bay crossing of the San Francisco-Oakland Bay Bridge cannot be attributed to relative displacements of the abutments in Oakland and Yerba Buena Island, but the motions of the Bay Bridge causing failure remain unknown. The steps in acceleration at Treasure Island present unusual strong-motion accelerogram processing problems, and modeling suggests that the velocity and displacement waveforms are contaminated by a spurious response of the filtering operations to the acceleration steps. A variety of coincidences suggests that the Treasure island accelerogram is the most likely strong-motion surrogate for the filled areas of the Marina District, for which no mainshock records are available, but the relative contributions of bad ground, poor construction and truly strong ground motion to damage in the Marina District will never by known in any quantitative way. The principal lesson of all of this is that until a concerted effort is mounted to instrument ground and structures that are likely to fail during earthquakes, our understanding of the very complex relationships between strong ground motion and earthquake damage will, in general, remain rudimentary, imprecise, and vague.

A site effect study in Acapulco, Guerrero, Mexico: Comparison of results from strong-motion and microtremor data

1992 ◽  
Vol 82 (2) ◽  
pp. 642-659 ◽  
Author(s):  
Carlos Gutierrez ◽  
Shri Krishna Singh
Keyword(s):  
Seismic Waves ◽  
Site Response ◽  
Nonlinear Behavior ◽  
Strong Motion ◽  
Site Effect ◽  
Seismic Gap ◽  
S Wave ◽  
Data Set ◽  
S Waves ◽  
The City

Abstract The city of Acapulco is located near or above the mature seismic gap of Guerrero along the Mexican subduction zone. With the purpose of studying the character of strong ground motion on soft sites, four digital accelerographs have been installed in the city on such sites. These instruments have been in operation since 1988. Two additional instruments, part of the Guerrero Accelerograph Array, are located on hard sites in the area. One of these, VNTA, has been in operation since 1985 and the other, ACAN, since 1989. These stations have recorded several earthquakes. We use data from eight events (4.2 ≤ M ≤ 6.9) to study spectral amplification of seismic waves at the soft sites with respect to VNTA. The S waves are amplified by a factor of 6 to 25 at the soft sites in a fairly broad range of frequencies; both the amplification and the frequency band over which it occurs depend upon the site. Although the largest earthquake in our data set (M = 6.9) gave rise to a peak horizontal acceleration exceeding 0.3 g at one of the soft sites, no clear evidence of nonlinear behavior of the subsoil is found. Spectral amplifications of S-wave coda are very similar to those of S waves. We also measured microtremors at the strong-motion sites. The microtremor spectra were interpreted, using reasonable assumptions, to test the feasibility of this technique in reproducing the spectral amplifications observed during earthquakes. Our results show that only a rough estimate of site response can be obtained from this technique, at least in Acapulco; caution is warranted in its use elsewhere.

Rupture history of the 1989 Loma Prieta, California, earthquake

1991 ◽  
Vol 81 (5) ◽  
pp. 1573-1602 ◽  
Author(s):  
Jamison H. Steidl ◽  
Ralph J. Archuleta ◽  
Stephen H. Hartzell
Keyword(s):  
Fault Plane ◽  
Strong Motion ◽  
Strike Slip ◽  
Nonlinear Method ◽  
Loma Prieta Earthquake ◽  
Shear Wave Speed ◽  
The North ◽  
Time Histories ◽  
Slip Displacement ◽  
Loma Prieta

Abstract Strong motion records of the 1989 Loma Prieta earthquake are inverted to determine a model of the rupture history. Uncorrected horizontal and vertical accelerograms are integrated to particle velocity time histories for 38 stations within an epicentral range of 75 km. The time histories are bandpassed filtered with corners at 0.05 and 1.0 Hz. These bandpassed time histories are inverted using a nonlinear method to solve for the distribution of slip amplitudes and rupture times at specified locations on the fault plane. The fault plane is specified a priori: 38 km long and 17 km wide, extending from 3 to 19 km depth at a constant dip of 70°. Starting models have rupture times based on constant rupture velocities of 2.5, 2.8, and 3.0 km/sec and uniform slip with rise times of 0.5, 1.0, 1.5, and 3.0 sec. The waveform inversion results show the strike-slip displacement is concentrated at the southern end of the rupture (rake = 156°) and the dip-slip displacement is concentrated at the northern end of the rupture (rake = 115°). The average total slip is partitioned almost equally between strike slip and dip slip (rake = 137°). The hypocentral area has an unusually small amount of slip with almost no slip in a region just to the north and up dip from the hypocenter. The rupture front is complex, propagating up dip to the south faster than it propagates to the north. The region of maximum strike slip to the southeast radiates simultaneously with the region of maximum dip slip to the northwest. The average rupture velocity is 3.0 km/sec, approximately 0.83 times the local shear wave speed. The calculated seismic moment is 3.5 ± 0.5 × 1026 dyne-cm.

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