Geology topics

John Boatwright

Publications and source records attributed to John Boatwright.

At least 19 recordsLinked to original sources

USGS2020

Peak ground motions and site response at Anza and Imperial Valley, California

Power spectra of shear-waves for eighteen earthquakes from the Anza-Imperial Valley region were inverted for source, mid-path Q, site attenuation and site response. The motivation was whether differences in site attenuation (parameterized as t*, r/cQ, where r is distance along ray path near the site, c is shear velocity and Q is the quality factor that parameterizes attenuation) and site response could be correlated with residuals in peak values of velocity or acceleration after removing the affect of distance-dependent attenuation. We decomposed spectra of S-waves from horizontal components of 18 earthquakes from 2010 to 2018 into a common source for each event with ω −2 spectral fall-off at high frequencies and then projected the residuals onto path and site terms following the methodology of Boatwright et al. (Bull Seismol Soc Am 81:1754–1782, 1991). The site terms were constrained to have an amplification at a particular frequency governed by V S30 at two of the sites which had downhole shear-wave logs. The 18 events, 3 < M < 4, had moments between approximately 10 20 and 10 22 dyne-cm, and stress drops between 1 and 100 bars. Average mid-crust attenuation had a Q of 844 reflecting the average path through the crystalline rock of the San Jacinto Mountains. t* for each station corresponded to the geologic environment such that stations on hard rock had low t* (e.g. stations KNW, PFO and RDM) a station in the San Jacinto fault zone (station SND) had a moderate t* of 0.035 s and stations in the Imperial Valley usually had higher t*s . Generally t* correlated with average amplification suggesting that sites characterized by low surface velocities and higher attenuation also have more amplification in the 1–6 Hz band. Residuals of peak values were determined by subtracting the prediction of Boore and Atkinson ( 2008 ). There is a correlation between average amplification and peak velocity, but not peak acceleration. Interestingly, there is less scatter at high values of amplification although there is also less data. Scatter in values of peak velocity and peak acceleration are higher at shorter compared to longer durations. When using a frequency-dependent form for Q , variances are higher, sometimes much higher; the dataset does not support frequency-dependent Q , which is not similar to results from the Imperial Valley and northeastern North America.

California↗

USGS2019

Directivity of M 3.1 earthquake near Anza, California and the effect on peak ground motion

We show the effect of rupture directivity on peak ground‐motion values for a moderate magnitude event at Anza, California, and neighboring stations at the Imperial Valley. The event was located near Borrego Springs on the west side of the Salton Sea and was well recorded at broadband stations near Anza, California, and at stations on the west side of the Imperial Valley. After correcting for regional attenuation, an anomalously large residual in peak motion was observed at station ERR just to the southeast of the epicenter. Using the algorithm from Boatwright (2007) , peak motions from the regional seismic networks in southern California were inverted to determine directivity, which was to the southeast along the trend of the San Jacinto fault toward station ERR. This algorithm uses peak values compiled for the ShakeMap system mostly at regional distances. It does not capture the main features of the source time function (STF) predicted by directivity. Consequently, we determined the second‐degree moments for this earthquake, which confirmed that station ERR has a shorter and higher STF compared to stations to the northwest suggesting rupture propagated to the southeast. The azimuthal distribution of local stations is sparse, but nevertheless the largest amplitudes (such as at station ERR) correlate well with the maximum in the radiation pattern and smaller values with the minima, which is the radiation pattern for SH plus the effect of directivity. Using the data from the analysis of the second‐degree moments, the characteristic length of the fault is 0.58 km, assuming an idealized unilateral extended rupture with a rupture time of 0.09 s. This yields an apparent rupture velocity of 6.4    km / s "> 6.4 km / s for an idealized model, which is super shear. This value is model dependent and would change if, for example, the rupture was bilateral. Although this value is even greater than the P ‐wave velocity, it supports the idea that the rupture velocity is super shear and would enhance the correlation between the peak motions and the radiation pattern.

California↗

USGS2019

κ0 and broadband site spectra in Southern California from source model-constrained inversion

Ground-motion modeling requires accurate representation of the earthquake source, path, and site. Site amplification is often modeled by VS30, the time-averaged shear-wave velocity of the top 30 meters of the Earth’s surface, though recent studies find that its ability to accurately predict site effects varies. Another measure of the site is κ0, the attenuation of high frequency energy near the site (Anderson & Hough, 1984). We develop a novel application of the Andrews (1986) method to simultaneously invert the spectra of 3,357 earthquakes in Southern California into source and site components. These earthquakes have magnitudes 2.5 to 5.72 and were recorded on 16 stations for a total of 52,297 records. We constrain the inversion with an individual earthquake demonstrating the most Brune-like shape to preserve the site spectra. We then solve for κ0 site amplification at each station in three frequency bands: 1-6 Hz, 6-14 Hz, and 14-35 Hz. The resulting values of κ0 range from 0.017 seconds at ANZA station PFO to 0.059 seconds at ANZA station SND. We compare our results with values of site κ0 from other studies as well as site residuals from GMPEs. We find good agreement between our site κ0 and previous studies in the region. We find that κ0 and high frequency site amplification (14-35 Hz band) correlates well with independent site residuals, making it a good first-order approximation for the effects of site attenuation or amplification on ground motion.

California↗

USGS2018

Reported investments in earthquake mitigation top $73 to $80 billion in the San Francisco Bay Area, California, since the 1989 Loma Prieta earthquake

The purpose of this report is to provide a compilation of structural retrofits and replacements of older buildings and infrastructure in the San Francisco Bay Area that have either been completed since 1989 or that are in progress as of October 2018. For the purposes of this report, all or parts of nine Bay Area counties were included: Alameda, Contra Costa, Marin, Napa, San Francisco, San Mateo, Santa Clara, Solano, and Sonoma. Santa Cruz County was not included. The compilation of 700 investments is presented as a table in the appendix. We consider this table as version 1, as we urge that those familiar with additional projects contact the report authors with information to update the table. In total, we have identified \$73 to \$80 billion in investments to retrofit or replace structures to mitigate the impacts of future San Francisco Bay Area earthquakes. These totals represent an average investment of \$2.5 to \$2.8 billion per year in retrofits and replacement of structures since 1989.

California↗

USGS2016

Faulting, damage, and intensity in the Canyondam earthquake of May 23, 2013

On Thursday evening, May 23, 2013 (0347 May 24 UTC), a moment magnitude (M w ) = 5.7 earthquake occurred northeast of Canyondam, California. A two-person team of U.S. Geological Survey scientists went to the area to search for surface rupture and to canvass damage in the communities around Lake Almanor. While the causative fault had not been identified at the time of the field survey, surface rupture was expected to have occurred just south of Lake Almanor, approximately 2–4 kilometers south of the epicenter. No surface rupture was discovered. Felt intensity among the communities around Lake Almanor appeared to vary significantly. Lake Almanor West (LAW), Lake Almanor Country Club (LACC), and Hamilton Branch (HB) experienced Modified Mercalli Intensity (MMI) ≥7, whereas other communities around the lake experienced MMI ≤6; the maximum observed intensity was MMI 8, in LAW. Damage in the high intensity areas consisted of broken and collapsed chimneys, ruptured pipes, and some damage to foundations and to structural elements within houses. Although this shaking damage is not usually expected for an M w 5.7 earthquake, the intensities at Lake Almanor Country Club correlate with the peak ground acceleration (38 percent g) and peak ground velocity (30 centimeters per second) recorded by the California Strong Motion Instrumentation Program accelerometer located at the nearby Lake Almanor Fire Station. The intensity distribution for the three hardest hit areas (LAW, LACC, and HB) appears to increase as the azimuth from epicenter to the intensity sites approaches the fault strike. The small communities of Almanor and Prattville on the southwestern shore of Lake Almanor experienced somewhat lower intensities. The town of Canyondam experienced a lower intensity as well, despite its location up-dip of the earthquake rupture. This report contains information on the earthquake itself, the search for surface rupture, and the damage we observed and compiled from other sources.

California↗

USGS2016

Earthquake outlook for the San Francisco Bay region 2014–2043

Using information from recent earthquakes, improved mapping of active faults, and a new model for estimating earthquake probabilities, the 2014 Working Group on California Earthquake Probabilities updated the 30-year earthquake forecast for California. They concluded that there is a 72 percent probability (or likelihood) of at least one earthquake of magnitude 6.7 or greater striking somewhere in the San Francisco Bay region before 2043. Earthquakes this large are capable of causing widespread damage; therefore, communities in the region should take simple steps to help reduce injuries, damage, and disruption, as well as accelerate recovery from these earthquakes.

California↗

USGS2016

Field survey of earthquake effects from the magnitude 4.0 southern Maine earthquake of October 16, 2012

The magnitude 4.0 earthquake that occurred on October 16, 2012, near Hollis Center and Waterboro in southwestern Maine surprised and startled local residents but caused only minor damage. A two-person U.S. Geological Survey (USGS) team was sent to Maine to conduct an intensity survey and document the damage. The only damage we observed was the failure of a chimney and plaster cracks in two buildings in East and North Waterboro, 6 kilometers (km) west of the epicenter. We photographed the damage and interviewed residents to determine the intensity distribution in the epicentral area. The damage and shaking reports are consistent with a maximum Modified Mercalli Intensity (MMI) of 5–6 for an area 1–8 km west of the epicenter, slightly higher than the maximum Community Decimal Intensity (CDI) of 5 determined by the USGS “Did You Feel It?” Web site. The area of strong shaking in East Waterboro corresponds to updip rupture on a fault plane that dips steeply east.

Connecticut, Maine, Massachusetts, New Hampshire, ↗

USGS2015

Ground motion observations of the 2014 South Napa earthquake

Ground motions of the South Napa earthquake (24 August 2014; M 6.0) were recorded at 19 stations within 20 km and 292 stations within 100 km of the rupture surface trace, generating peak ground motions in excess of 50% g and 50  cm/s in and near Napa Valley. This large dataset allows us to compare the ground motion from the earthquake to existing ground‐motion prediction equations (GMPEs) in considerable detail. Using the ground‐motion data compiled and reported by ShakeMap ( Wald et al. , 2000 ), we examine the peak ground acceleration (PGA) and peak ground velocity (PGV), as well as the pseudospectral acceleration (PSA) at periods of 0.3, 1.0, and 3.0 s. At the higher frequencies, especially PGA, data recorded at close distances (within &sim;20  km) are very consistent with the GMPEs, implying a stress drop for this event similar to the median for California, that is, 5 MPa ( Baltay and Hanks, 2014 ). At all frequencies, the attenuation with distance is stronger than the GMPEs would predict, which suggests the attenuation in the Napa and San Francisco Bay delta region is stronger than the average attenuation in California. The spatial plot of the ground‐motion residuals is positive to the north, in both Napa and Sonoma Valleys, consistent with increases in amplitude expected from both the directivity and basin effects. More interestingly, perhaps, there is strong ground motion to the south in the along‐strike direction, particularly for PSA at 1.0 s. These strongly positive residuals align with an older, Quaternary fault structure associated with the Franklin or Southampton fault, potentially indicating a fault‐zone‐guided wave.

California↗

USGS2015

The Mw6.0 24 August 2014 South Napa earthquake

The M w 6.0 South Napa earthquake, which occurred at 10:20 UTC 24 August 2014 was the largest earthquake to strike the greater San Francisco Bay area since the M w 6.9 1989 Loma Prieta earthquake. The rupture from this right‐lateral earthquake propagated mostly unilaterally to the north and up‐dip, directing the strongest shaking toward the city of Napa, where peak ground accelerations (PGAs) between 45% g and 61% g were recorded and modified Mercalli intensities (MMIs) of VII–VIII were reported. Tectonic surface rupture with dextral slip of up to 46 cm was observed on a 12.5 km long segment, some of which was along a previously mapped strand of the West Napa fault system, although the rupture extended to the north of the mapped Quaternary strand. Modeling of seismic and geodetic data suggests an average coseismic slip of 50 cm, with a maximum slip of about 1 m at depths of 10–11 km. We observed up to 35 cm of afterslip along the surface trace in the week following the mainshock, primarily along the southern half of the surface rupture that experienced relatively little coseismic offset. Relocation of the sparse aftershock sequence suggests en echelon southwest‐ and northeast‐dipping fault planes, reflective of the complex fault geometry in this region. The Napa basin and historic and late Holocene alluvial flood deposits in downtown Napa amplified the ground motions there. Few ground failures were mapped, reflecting the dry season (as well as a persistent drought that had lowered the groundwater table) and the short duration of strong shaking in the epicentral area.

California↗

USGS2014

Key recovery factors for the August 24, 2014, South Napa Earthquake

Through discussions between the Federal Emergency Management Agency (FEMA) and the U.S. Geological Survey (USGS) following the South Napa earthquake, it was determined that several key decision points would be faced by FEMA for which additional information should be sought and provided by USGS and its partners. This report addresses the four tasks that were agreed to. These tasks are (1) assessment of ongoing fault movement (called afterslip) especially in the Browns Valley residential neighborhood, (2) assessment of the shaking pattern in the downtown area of the City of Napa, (3) improvement of information on the fault hazards posed by the West Napa Fault System (record of past earthquakes and slip rate, for example), and (4) imagery acquisition and data processing to provide overall geospatial information support to FEMA.

California↗

USGS2013

Site Response and Basin Waves in the Sacramento–San Joaquin Delta, California

The Sacramento–San Joaquin Delta is an inland delta at the western extent of the Central Valley. Levees were built around swampy islands starting after the Civil War to reclaim these lands for farming. Various studies show that these levees could fail in concert from shaking from a major local or regional earthquake resulting in salty water from the San Francisco Bay contaminating the water in the Delta. We installed seismographs around the Delta and on levees to assess the contribution of site response to the seismic hazard of the levees. Cone penetrometer testing shows that the upper 10 s of meters of soil in the Delta have shear‐wave velocities of about 200 m/s, which would give a strong site response. Seismographs were sited following two strategies: pairs of stations to compare the response of the levees to nearby sites, and a more regional deployment in the Delta. Site response was determined in two different ways: a traditional spectral ratio (TSR) approach of S waves using station BDM of the Berkeley Digital Seismic Net as a reference site, and using SH / SV ratios of noise (or Nakamura’s method). Both estimates usually agree in spectral character for stations whose response is dominated by a resonant peak, but the most obvious peaks in the SH / SV ratios usually are about two‐thirds as large as the main peaks in the TSRs. Levee sites typically have large narrow resonances in the site response function compared to sites in the farmland of the Delta. These resonances, at a frequency of about 1–3 Hz, have amplitudes of about 15 with TSR and 10–12 with Nakamura’s method. Sites on farmland in the Delta also have amplifications, but these are typically broader and not as resonant in appearance. Late (slow) Rayleigh waves were recorded at stations in the Delta, have a dominant period of about one second, and are highly monochromatic. Results from a three‐station array at the Holland Marina suggest that they have a phase velocity of about 600 m/s and arrive at about the same azimuth as the straight‐line back azimuth to the source. A dispersion curve determined for the basin or valley waves yields a shallow velocity profile that increases from about 350 m/s in the upper 0.2 km to about 1.1 km/s at a depth of about 2 km.

California↗

USGS2012

Source characteristics of the Loma Prieta, California, Earthquake of October 18, 1989 from global digital seismic data

Displacement, velocity and acceleration records of P and SH body waves recorded at teleseismic distances are analysed to determine the static and dynamic source parameters of the Loma Prieta, California earthquake of October 18, 1989 ( m b 6.6, M s 7.1). Three distinct bursts of energy corresponding to three subevents can be recognized in most records. The displacement waveforms indicate that the first subevent contributes negligible moment while the largest releases of moment and energy are controlled by the second and third subevents. The second and third subevents are located north and south of the initial nucleation. A fourth small subevent needed to model later features of the P waveforms suggests that slow slip continued after the major releases of energy occurred. The waveforms are fit with a fault plane solution having strike 130°, dip 65° and slip 140° for all the subevents. The focal depths of the two major subevents are 16 and 12 km, and their asperity radii are 4.0 and 6.0 km, respectively. The seismic moment, M 0 , is 2.2×10 26 dyne-cm. From spectral analysis of teleseismic velocity, the radiated energy, E s , is estimated to be 1.1×10 22 dyne-cm, implying an apparent stress of 15 bars. From the high-frequency level of the teleseismic acceleration spectrum and a rupture area of 440 km 2 , we derive a dynamic stress drop of 51 bars.

California↗

USGS2012

Long-term creep rates on the Hayward Fault: Evidence for controls on the size and frequency of large earthquakes

The Hayward fault (HF) in California exhibits large (Mw 6.5–7.1) earthquakes with short recurrence times (161±65 yr), probably kept short by a 26%–78% aseismic release rate (including postseismic). Its interseismic release rate varies locally over time, as we infer from many decades of surface creep data. Earliest estimates of creep rate, primarily from infrequent surveys of offset cultural features, revealed distinct spatial variation in rates along the fault, but no detectable temporal variation. Since the 1989 Mw 6.9 Loma Prieta earthquake (LPE), monitoring on 32 alinement arrays and 5 creepmeters has greatly improved the spatial and temporal resolution of creep rate. We now identify significant temporal variations, mostly associated with local and regional earthquakes. The largest rate change was a 6‐yr cessation of creep along a 5‐km length near the south end of the HF, attributed to a regional stress drop from the LPE, ending in 1996 with a 2‐cm creep event. North of there near Union City starting in 1991, rates apparently increased by 25% above pre‐LPE levels on a 16‐km‐long reach of the fault. Near Oakland in 2007 an Mw 4.2 earthquake initiated a 1–2 cm creep event extending 10–15 km along the fault. Using new better‐constrained long‐term creep rates, we updated earlier estimates of depth to locking along the HF. The locking depths outline a single, &sim;50‐km‐long locked or retarded patch with the potential for an Mw&sim;6.8 event equaling the 1868 HF earthquake. We propose that this inferred patch regulates the size and frequency of large earthquakes on HF.

California↗

USGS2011

Regional spectral analysis of three moderate earthquakes in Northeastern North America

We analyze Fourier spectra obtained from the horizontal components of broadband and accelerogram data from the 1997 Cap-Rouge, the 2002 Ausable Forks, and the 2005 Rivière-du-Loup earthquakes, recorded by Canadian and American stations sited on rock at hypocentral distances from 23 to 602 km. We check the recorded spectra closely for anomalies that might result from site resonance or source effects. We use Beresnev and Atkinson’s (1997) near-surface velocity structures and Boore and Joyner’s (1997) quarter-wave method to estimate site response at hard- and soft-rock sites. We revise the Street et al. (1975) model for geometrical spreading, adopting a crossover distance of r o =50 km instead of 100 km. We obtain an average attenuation of Q =410±25f 0.50±0.03 for S+L g +surface waves with ray paths in the Appalachian and southeastern Grenville Provinces. We correct the recorded spectra for attenuation and site response to estimate source spectral shape and radiated energy for these three earthquakes and the 1988 M 5.8 Saguenay earthquake. The Brune stress drops range from 130 to 419 bars, and the apparent stresses range from 39 to 63 bars. The corrected source spectral shapes of these earthquakes are somewhat variable for frequencies from 0.2 to 2 Hz, falling slightly below the fitted Brune spectra.

Bulletin of the Seismological Society of America↗

USGS2010

The 2007 M5.4 Alum Rock, California, earthquake: Implications for future earthquakes on the central and southern Calaveras Fault

[1] The similarity of seismograms recorded by two seismic stations demonstrate that the 31 October 2007 moment magnitude M 5.4 Alum Rock earthquake is a repeat of a 1955 M L 5.5 earthquake. Both occurred on Oppenheimer et al.'s (1990) Zone V “stuck patch” on the central Calaveras fault, providing new support for their model of Calaveras fault earthquake activity. We suggest that Zone V fails only in a family of recurring M ∼ 5.4–5.5 earthquakes. The 1955 and 2007 earthquakes are the penultimate and ultimate Zone V events. Earthquakes in 1891 and 1864 are possible earlier Zone V events. The next Zone V event is not expected in the next few decades, assuming a time‐dependent recurrence model: the mean forecast date is 2064 (2035–2104, 95% confidence range). We further suggest that Zones I, II, III, and IV fail in recurring M ∼ 5.1–5.3, M ∼ 5.6–5.8, M ∼ 6.1–6.3, and M ∼ 4.9–5.0 earthquakes, respectively. If our earthquake recurrence model is correct, the next Zone I event is overdue and could occur anytime, and M 5–6 earthquakes should not occur on Zones II, III, and IV before 2014, 2012, and 2026, respectively. We cannot rule out the possibility that Zone VI, which lies at the southern end of the Mission Seismic Trend, where the southern Hayward and central Calaveras faults appear to connect at depth, fails aseismically or in large events on the southern Hayward fault, such as last occurred in 1868, or in large events on the adjoining northern Calaveras fault segment.

California↗

USGS2010

Rupture directivity of moderate earthquakes in northern California

We invert peak ground velocity and acceleration (PGV and PGA) to estimate rupture direction and rupture velocity for 47 moderate earthquakes (3.5≥M≥5.4) in northern California. We correct sets of PGAs and PGVs recorded at stations less than 55–125 km, depending on source depth, for site amplification and source–receiver distance, then fit the residual peak motions to the unilateral directivity function of Ben-Menahem (1961). We independently invert PGA and PGV. The rupture direction can be determined using as few as seven peak motions if the station distribution is sufficient. The rupture velocity is unstable, however, if there are no takeoff angles within 30° of the rupture direction. Rupture velocities are generally subsonic (0.5β–0.9β); for stability, we limit the rupture velocity at v=0.92β, the Rayleigh wave speed. For 73 of 94 inversions, the rupture direction clearly identifies one of the nodal planes as the fault plane. The 35 strike-slip earthquakes have rupture directions that range from nearly horizontal (6 events) to directly updip (5 events); the other 24 rupture partly along strike and partly updip. Two strike-slip earthquakes rupture updip in one inversion and downdip in the other. All but 1 of the 11 thrust earthquakes rupture predominantly updip. We compare the rupture directions for 10 M≥4.0 earthquakes to the relative location of the mainshock and the first two weeks of aftershocks. Spatial distributions of 8 of 10 aftershock sequences agree well with the rupture directivity calculated for the mainshock.

California↗

USGS2008

Modified Mercalli Intensity Maps for the 1868 Hayward Earthquake Plotted in ShakeMap Format

To construct the Modified Mercalli Intensity (MMI) ShakeMap for the 1868 Hayward earthquake, we started with two sets of damage descriptions and felt reports. The first set of 100 sites was compiled by A.A. Bullock in the Lawson (1908) report on the 1906 San Francisco earthquake. The second set of 45 sites was compiled by Toppozada et al. (1981) from an extensive search of newspaper archives. We supplemented these two sets of reports with new observations from 30 sites using surveys of cemetery damage, reports of damage to historic adobe structures, pioneer narratives, and reports from newspapers that Toppozada et al. (1981) did not retrieve. The Lawson (1908) and Toppozada et al. (1981) compilations and our contributions are assembled in the Site List.

Open-File Report↗

USGS2006

A simple model for strong ground motions and response spectra

A simple model for the description of strong ground motions is introduced. The model shows that response spectra can be estimated by using only four parameters of the ground motion, the RMS acceleration, effective duration and two corner frequencies that characterize the effective frequency band of the motion. The model is windowed band-limited white noise, and is developed by studying the properties of two functions, cumulative squared acceleration in the time domain, and cumulative squared amplitude spectrum in the frequency domain. Applying the methods of random vibration theory, the model leads to a simple analytical expression for the response spectra. The accuracy of the model is checked by using the ground motion recordings from the aftershock sequences of two different earthquakes and simulated accelerograms. The results show that the model gives a satisfactory estimate of the response spectra.

Earthquake Engineering and Structural Dynamics↗