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Kulkarni et al. (2013; hereafter, Kulkarni2013) present a detailed statistical analysis of records of possible repeat great earthquakes on the Cascadia subduction zone, offshore of Vancouver Island, Washington, Oregon, and northern California. The data set they analyze is derived from turbidite cores collected off the Washington, Oregon, and northern California coasts (Goldfinger et al. , 2012; hereafter, Goldfinger2012). They conclude that there is a 65% probability that the data are in fact clustered, as previous authors have speculated. This means that the cluster hypothesis does not meet the usual 95% threshold for acceptance of a hypothesis, although they then engage in a fairly complicated second‐order analysis which concludes the data are significantly clustered. They acknowledge that this may not be a unique interpretation, and essentially invite alternative models. > We recognize that the total reliance on the interpretations of Goldfinger et al. (2012) begs the question, would we reach the same conclusions if the turbidite data were interpreted differently by another set of eyes? Although the Goldfinger et al. (2012) study has undergone extensive review, that question cannot be answered until future interpretations become available. (Kulkarni2013, p. 16) What follows is my attempt to present an alternative interpretation, one with rather different implications for the seismic hazard in the Pacific Northwest. (For reference, the top half of fig. 2 from Kulkarni2013 is plotted below as Fig. 1.) Figure 1. Copied from the top half of figure 2 from Kulkarni et al. (2013). The height of each bar reflects the average turbidite mass observed offshore, the width of the bars represents the uncertainty in the time of the events. I have added all four segment B events from Goldfinger et al. (2012), shown here as small open boxes, approximately located. (The height and width of these boxes does not represent turbidite volume or uncertainty.) In summary, my argument …

Forty-two portable digital instruments were deployed across the Santa Clara Valley from June until early November 1998; this array recorded 14 small and moderate local events and 7 large teleseismic events. We analyze the ground motion from these events to determine station delays and relative site amplification within the Valley. P waves from an event at the southern edge of the valley are early (Δ t > -0.35 sec) at stations over an axial ridge in the basement interface in the middle of the valley, but late (Δ t < 0.20 sec) for stations over the Cupertino and Evergreen basins to either side. The S -wave delays are approximately twice as large. Teleseismic P -waves from an M = 7.0 event beneath the Bonin Islands show a similar pattern in travel-time delays. The P waves are amplified by factors of 1.5-3 for frequencies below 2 Hz at stations within either basin, compared with stations on the axial ridge. The P -wave coda appear enhanced at 2-3 sec, but coda Q estimates at frequencies from 0.2 to 1.1 Hz are not markedly different at stations over the basin compared with stations on the ridge with the possible exceptions of consistently high values over the northern end of the Evergreen Basin. We invert the S -wave spectra for site-specific attenuation and amplification from the 14 local events by assuming a common source spectra for each event, 1/ r geometrical spreading, and constraining the inversion using the 30-m velocity profile at four stations in the array. The largest amplifications occurred in the 1- to 6-Hz band at stations near the northwest edge of the Evergreen basin. While the highest amplifications occur at stations with the lowest S -wave velocities, the scatter obscures the correlation between velocity and amplification. The stations in the basins are characterized by higher attenuation than the stations on the basement ridge. Manuscript received 2 July 2001.

The Trichinella tsJ5 gene is preferentially expressed in muscle larvae of Trichinella spiralis and encodes a novel protein. Previous observations have shown tsJ5 to be expressed at higher levels in encapsulating species than in non-encapsulating species and down-regulation of gene expression in T. pseudospiralis to be correlated with a lower protein abundance in the muscle larva of this species. In the present study we have determined the full-length cDNA sequence of the tsJ5 homologue in T. pseudospiralis (tpJ5). Antigens recognised by an anti-J5 antibody are found on the cuticular surface of both T. spiralis and T. pseudospiralis muscle larvae, as well as in the body wall muscle. We show that both the TSJ5 and TPJ5 proteins are found in the excretory/secretory fractions collected from muscle larva cultured in vitro and that despite the absence of a typical N-terminal signal sequence, secretion of pTSJ5 is mediated through the classical ER/Golgi secretory pathway.

We present SEA99, a revised predictive relation for geometric mean horizontal peak ground acceleration and 5%-damped pseudovelocity response spectrum, appropriate for estimating earthquake ground motions in extensional tectonic regimes, which we demonstrate to have lower ground motions than other tectonic regimes. SEA99 replaces SEA96, a relation originally derived by Spudich et al. (1996, 1997). The data set used to develop SEA99 is larger than that for SEA96, and minor errors in the SEA96 data set have been corrected. In addition, a one-step regression method described by Joyner and Boore (1993, 1994) was used rather than the two-step method of Joyner and Boore (1981). SEA99 has motions that are as much as 20% higher than those of SEA96 at short distances (5-30 km), and SEA99's motions are about 20% lower than SEA96 at longer periods (1.0-2.0 sec) and larger distance (40-100 km). SEA99 dispersions are significantly less than those of SEA96. SEA99 rock motions are on the average 20% lower than motions predicted by Boore et al. (1994) except for short distances at periods around 1.0 sec, where SEA99 motions exceed those predicted by Boore et al. (1994) by as much as 10%. Comparison of ground motions from normal-faulting and strike-slip events in our data set indicates that normal-faulting horizontal ground motions are not significantly different from extensional regime strike-slip ground motions.

Chronic Fatigue Syndrome (CFS) is characterized by debilitating fatigue, somatic symptoms and cognitive impairment. An infectious basis has been proposed; candidate agents include enteroviruses, herpesviruses, retroviruses and Borna disease virus (BDV), a novel neurotropic virus associated with neuropsychiatric disorders. Sera and peripheral blood mononuclear cells (PBMC) from Swedish CFS patients were assayed for evidence of infection using ELISA and Western immunoblot for detection of antibodies to BDV proteins N, P and gp18; and using nested reverse transcriptase polymerase chain reaction (RT-PCR) for detection of BDV N- and P-gene transcripts. No specific immunoreactivity to BDV proteins was found in sera from 169 patients or 62 controls. No BDV N- or P-gene transcripts were found through RT-PCR analysis of PBMC from 18 patients with severe CFS. These results do not support a role for BDV in pathogenesis of CFS.

Development of the infective L1 larva of Trichinella spiralis occurs as an intracellular parasite of skeletal muscle and leads to the dedifferentiation of the host cell. A novel Trichinella gene, tsJ5, has been identified from a cDNA library screen for sequences encoding Trichinella proteins related to the myogenic bHLH factors. The tsJ5 gene is developmentally regulated, showing preferential expression in the infective muscle stage larva. The product of the tsJ5 gene is not a bHLH protein but represents a novel protein with properties in common with some myogenic repressors. A recombinant TsJ5 protein affects the formation of MyoD:DNA complexes in vitro.

We present a new predictive relation for horizontal peak ground acceleration and 5% damped pseudo-velocity response spectrum appropriate for predicting earthquake ground motions in extensional tectonic regimes. This new empirical relation, which we denote “Sea96,” was originally derived by Spudich et al. (1996) as part of a project to estimate seismic hazard at the site of a proposed nuclear waste repository at Yucca Mountain, Nevada. Because of the length and relative inaccessibility of that report, we are briefly presenting the Sea96 relation and its derivation here. We developed our relation based on data from extensional regime earthquakes having moment magnitude M > 5.0 recorded at distances less than 105 km. Extensional regions are regions in which the lithosphere is expanding areally. This areal expansion is the result of applied forces that yield a state of stress for which Sv > SHmax > SHmin , where Sv , SHmax , and SHmin represent principal...

Human cytomegalovirus (CMV) encodes a unique serine proteinase that is required in the maturation of the viral capsid. The CMV proteinase can undergo autocatalytic activation and is subject to proteolytic self-inactivation. Mutant enzyme forms were prepared to eliminate the initial autoprocessing site and thus form an active single-chain protein for structure-function studies. Two mutants of CMV proteinase were cloned and expressed in Escherichia coli. The A143V mutant was a conservative substitution at the first internal cleavage site. The S132A mutant modified one of the triad of residues responsible for catalytic activity. Through the use of computer-controlled high-cell-density fermentations the mutant proteins were expressed in E. coli at approximately 170 mg/L as both soluble (approximately 40% of total) and inclusion-body forms (approximately 60% of total). The soluble enzyme was purified by standard methods; inclusion-body protein was isolated by standard methods after refolding and solubilization in guanidine or urea. Sedimentation equilibrium and sedimentation velocity analyses reveal that the enzyme undergoes concentration-dependent aggregation. It exhibits a monomer dimer equilibrium (Kd = 1 microM) at low concentrations and remains dimeric at high concentrations (28 mg/ml). Differential scanning calorimetry data for protein thermal unfolding fit best to a non-two-state model with two components (Tm = 52.3 and 55.3 degrees C) which subsequently aggregate upon unfolding. Analysis of the short-UV circular dichroism spectra of protein forms resulting from expression as soluble molecules (not refolded) reveals that the two mutants have very similar secondary structures which comprise a mixed structural motif of 20% alpha-helix, 26% beta-sheet, and 53% random coil. Though soluble and active (A143V mutant only), CD analysis revealed that protein refolded from inclusion bodies did not exhibit spectra identical to that of protein expressed only in soluble form.

Earthquake prediction is inherently statistical. Although some people continue to think of earthquake prediction as the specification of the time, place, and magnitude of a future earthquake, it has been clear for at least two decades that this is an unrealistic and unreasonable definition. The reality is that earthquake prediction starts from long-term forecasts of place and magnitude, with very approximate time constraints, and progresses, at least in principle, to a gradual narrowing of the time window as data and understanding permit. The analogy to catching a rabbit in an overgrown confined field may be appropriate. You do not just start out looking for the rabbit, you instead build a fence dividing the field in two and then decide which half the rabbit is in, thereby gaining one bit of information. You iterate this process until you have located the rabbit “close enough for practical purposes.” This is approximately how earthquake prediction proceeds in the real world, with time and position along a fault comprising the two dimensions of the search. (I assume here that we are considering for the moment only large earthquakes, that is those capable of inflicting serious damage on a regional scale; in California this means events of about M 6.7 and larger.) This more realistic perspective on the problem lays to rest the “red herring” that “earthquake predictions might do more harm than earthquakes.” These imaginary concerns are predicated on the fantasy of a prediction that precisely specifies time, place, and magnitude; in the real world a progression of probabilities that narrows the space-time window in small steps clearly carries no such threat. [E]arthquake prediction starts from long-term forecasts of place and magnitude, with very approximate time constraints, and progresses... to a gradual narrowing of the time window as data and understanding permit. In the …

We have plotted the cumulative seismic slip projected onto a vertical plane for earthquakes occurring during the last 20 years along 210 km of the San Andreas fault that includes the section that moved in the Loma Prieta earthquake. These plots illustrate the differences in depth and character of the seismicity between the locked and creeping portions of the fault or fault zone and define the segment upon which the Loma Prieta earthquake occurred. Working by analogy from the relation between pre-main shock microseismicity and presumed main shock slip regions at Parkfield and Loma Prieta, we identify a segment on the San Francisco Peninsula where we believe the M 7 1838 earthquake occurred, and which we believe may have accumulated sufficient strain that rupture should be expected in the coming decades.

BACKGROUND: Risk factors for mother-to-child transmission of hepatitis C virus (HCV) are poorly quantified. METHODS: We conducted a European multicenter prospective study of HCV-infected pregnant women and their infants. Children with > or =2 positive HCV RNA polymerase chain reaction test results and/or anti-HCV antibodies after 18 months of age were considered to be infected. RESULTS: The overall HCV vertical transmission rate was 6.2% (95% confidence interval [CI], 5.0%-7.5%; 91/1479). Girls were twice as likely to be infected as boys (adjusted odds ratio [OR], 2.07 [95% CI, 1.23-3.48]; P=.006). There was no protective effect of elective cesarean section (CS) delivery on HCV vertical transmission (adjusted OR, 1.46 [95% CI, 0.86-2.48]; P=.16). HCV/human immunodeficiency virus-coinfected women more frequently transmitted HCV than did women with HCV infection only, although the difference was not statistically significant (adjusted OR, 1.82 [95% CI, 0.94-3.52]; P=.08). Maternal history of injection drug use, prematurity, and breast-feeding were not significantly associated with transmission. Transmission occurred more frequently from viremic women, but it also occurred from a few nonviremic women. CONCLUSIONS: Our results strongly suggest that women should neither be offered an elective CS nor be discouraged from breast-feeding on the basis of HCV infection alone. The sex association is an intriguing finding that probably reflects biological differences in susceptibility or response to infection.

Kuratli, S., Lindh, J. G., Gottstein, B., Smith, D. F., and Connolly, B. 1999. Trichinella spp.: Differential expression of two genes in the muscle larva of encapsulating and nonencapsulating species. Experimental Parasitology 93, 153-159. The expression of the two genes tsmyd-1 and tsJ5 was studied in the muscle stage larva of three different species of Trichinella. T. spiralis and T. britovi are both encapsulating species, while T. pseudospiralis is a nonencapsulating species. Expression of tsJ5 is developmentally regulated in T. spiralis and has been shown in this study to be down-regulated in the T. pseudospiralis muscle larva compared with the other two species. Immunoblot analysis has also revealed that the relative abundance of the protein product of this gene, TSJ5, is lower in T. pseudospiralis muscle larvae. It has previously been shown that expression of tsmyd-1 is not developmentally regulated in T. spiralis (Connolly et al. 1996). In contrast, expression of this gene is slightly increased in the muscle larvae of T. pseudospiralis. Southern analysis of genomic DNA from the three Trichinella species shows that both genes are highly conserved.

Recently, we found a serum acylcarnitine (ACR) deficiency in Japanese patients with chronic fatigue syndrome (CFS). To clarify whether this ACR abnormality is a characteristic of CFS or not, we also studied the levels of serum carnitine in Swedish subjects. Both serum ACR and free carnitine (FCR) levels in normal healthy subjects were quite different between Japanese (n=131) and Swedish people (n=46) (p

Development of the infective L1 larva of Trichinella spiralis occurs as an intracellular parasite of skeletal muscle and leads to the dedifferentiation of the host cell. A novel Trichinella gene, tsJ5, has been identified from a cDNA library screen for sequences encoding Trichinella proteins related to the myogenic bHLH factors. The tsJ5 gene is developmentally regulated, showing preferential expression in the infective muscle stage larva. The product of the tsJ5 gene is not a bHLH protein but represents a novel protein with properties in common with some myogenic repressors. A recombinant TsJ5 protein affects the formation of MyoD:DNA complexes in vitro.

Methods: Twelve patients with idiopathic PD were implanted with a drug pump and an investigational catheter (Medtronic Inc) leading into the lateral ventricle. Patients were divided into 3 dose cohorts (0.2, 1.5 or 5 μg PDGF/day) and received either PDGF or placebo (buffer, 1 patient/cohort) for 12 days, after which all patients received buffer and were followed up to Day 85. Study objectives included continuous safety and tolerability assessments and UPDRS, MADRS, MMT, EQ5-D and DAT-binding (PET) assessments pre-treatment and at the end-of study.

To study the effect of smoking on plasma antioxidants with and without antioxidant vitamin nutratherapy.Chronic smokers (n = 10, 16 +/- 4 cigarettes a day) and nonsmokers (n = 17) of both sexes were recruited from patients with arthritis-like symptoms. After baseline studies of plasma antioxidant vitamins Q (ubiquinone) and E (alpha-tocopherol) and essential fatty acids (EFA, vitamin F), three months' nutratherapy with vitamins Q (90 mg) and E (350 mg) was administered and plasma reanalyzed.No sex differences were seen in smoking habits or plasma nutrients. Smokers had normal Q (0.71 +/- 0.07 mg/L) but depressed E (9.4 +/- 0.6 mg/L, P0.01). EFA were the same in both groups. Nutratherapy increased Q by about 90% in both groups and E by 47% in smokers and 101% in nonsmokers (P0.01). In nonsmokers, nutratherapy protected omega-3 fatty acids (vitamin F1)-plasma docosahexaenoic acid increased by 39%. The vitamin F index (omega-6:omega-3, ratio) remained unchanged in the smokers but decreased in the nonsmokers and became related to the individual plasma vitamin Q but not to vitamin E.There was no difference between smokers and nonsmokers before nutratherapy. Nonsmokers may have suffered from passive smoking. After nutratherapy the quantitatively most important antioxidant, ie, vitamin E, increased more in nonsmokers than in smokers. This resulted in less vitamin F1 peroxidation. Nutratherapy cannot overcome disadvantages associated with smoking. Nonsmokers might achieve an antioxidant protection with nutratherapy, which could mean a possible reduced risk of developing cardiovascular disease.

The capacity of the nucleocapsid protein of HBV to function as a T-cell independent antigen in man was studied. When T-cell depleted B-cell cultures were challenged with E coli-derived HBcAg, anti-HBc production was registered in culture supernatants from the majority of chronic HBsAg carriers in a quiescent stage of disease. In contrast, similarly prepared and stimulated cultures from donors with natural acquired immunity to hepatitis B or HB-susceptible controls were non-responsive. Addition of autologous T-cells effectively restored anti-HBc responsiveness in T-cell depleted B-cell cultures from HB-immune donors, demonstrating the T-cell dependency for anti-HBc induction in natural HBV-infection.

The capacity of the nucleocapsid protein of HBV to function as a T-cell independent antigen in man was studied. When T-cell depleted B-cell cultures were challenged with E coli-derived HBcAg, anti-HBc production was registered in culture supernatants from the majority of chronic HBsAg carriers in a quiescent stage of disease. In contrast, similarly prepared and stimulated cultures from donors with natural acquired immunity to hepatitis B or HB-susceptible controls were non-responsive. Addition of autologous T-cells effectively restored anti-HBc responsiveness in T-cell depleted B-cell cultures from HB-immune donors, demonstrating the T-cell dependency for anti-HBc induction in natural HBV-infection.

In order to better understand the interaction between the inverted repeats (IRs) of the transposon Tn3 and Tn3 transposase, we have looked at the effects of mutations within the IRs on binding of transposase and transposition immunity. Binding of transposase to mutated IRs was measured using a site-specific nitrocellulose filter binding assay and by DNase I protection studies. Transposition immunity was measured in vivo using a transposition mating-out assay. The most important determinants for binding of transposase are present within the inside 21 base-pairs of the IR and several single base-pair mutations significantly reduce binding. Base-pair mutations which do not effect binding have strong negative effects on transposition immunity indicating that simple binding of transposase to the IR is not sufficient for the establishment of transposition immunity.

We present SEA99, a revised predictive relation for geometric mean horizontal peak ground acceleration and 5%-damped pseudovelocity response spec- trum, appropriate for estimating earthquake ground motions in extensional tectonic regimes, which we demonstrate to have lower ground motions than other tectonic regimes. SEA99 replaces SEA96, a relation originally derived by Spudich et al. (1996, 1997). The data set used to develop SEA99 is larger than that for SEA96, and minor errors in the SEA96 data set have been corrected. In addition, a one-step regression method described by Joyner and Boore (1993, 1994) was used rather than the two-step method of Joyner and Boore (1981). SEA99 has motions that are as much as 20% higher than those of SEA96 at short distances (5-30 km), and SEA99's motions are about 20% lower than SEA96 at longer periods (1.0-2.0 sec) and larger distance (40-100 km). SEA99 dispersions are significantly less than those of SEA96. SEA99 rock motions are on the average 20% lower than motions predicted by Boore et al. (1994) except for short distances at periods around 1.0 sec, where SEA99 motions exceed those predicted by Boore et al. (1994) by as much as 10%. Com- parison of ground motions from normal-faulting and strike-slip events in our data set indicates that normal-faulting horizontal ground motions are not significantly different from extensional regime strike-slip ground motions.

How do we know the Sun will rise tomorrow? Hume's concern raises two questions: the problem of empirical inference was solved in this century by Popper; an approach to the stability of nature in time is outlined here.

Examination of main shock and microearthquake data from the Calaveras fault during the last 20 years reveals that main shock hypocenters occur at depths of 8–9 km near the base of the zone of microearthquakes. The spatial pattern of pre-main shock microseismicity surrounding the Coyote Lake and Morgan Hill hypocenters is similar to the pattern of the post-main shock microseismicity. Microseismicity extends between depths of 4 and 10 km and defines zones of concentrated microseismicity and aseismic zones. Estimates of the fault regions which slipped during the Coyote Lake and Morgan Hill earthquakes as derived from seismic radiation coincide with zones which are otherwise aseismic. We propose that these persistent aseismic zones represent stuck patches which slip only during moderate earthquakes. From the pattern of microearthquake locations we recognize six aseismic zones where we expect future main shocks will rupture the Calaveras fault. From an analysis of historic seismic data we establish the main shock rupture history for each aseismic zone and identify two zones that are the most likely sites for the next M > 5 earthquakes. The first zone is located near Gilroy and was last ruptured by a M5.2 earthquake in 1949. The second zone is located south of Calaveras Reservoir and north of the 1988 M5.1 Alum Rock earthquake. It has not slipped seismically since at least 1903, and the size of the aseismic region is sufficiently large to sustain a M5.5 earthquake.

A reanalysis of the available data for the 1966 Parkfield, California, earthquake (ML=512) suggests that although the ground breakage and aftershocks extended about 40 km along the San Andreas Fault, the initial dynamic rupture was only 20 to 25 km in length. The foreshocks and the point of initiation of the main event locate at a small bend in the mapped trace of the fault. Detailed analysis of the P-wave first motions from these events at the Gold Hill station, 20 km southeast, indicates that the bend in the fault extends to depth and apparently represents a physical discontinuity on the fault plane. Other evidence suggests that this discontinuity plays an important part in the recurrence of similar magnitude 5 to 6 earthquakes at Parkfield.Analysis of the strong-motion records suggests that the rupture stopped at another discontinuity in the fault plane, an en-echelon offset near Gold Hill that lies at the boundary on the San Andreas Fault between the zone of aseismic slip and the locked zone on which the great 1857 earthquake occurred. Foreshocks to the 1857 earthquake occurred in this area (Sieh, 1978), and the epicenter of the main shock may have coincided with the offset zone. If it did, a detailed study of the geological and geophysical character of the region might be rewarding in terms of understanding how and why great earthquakes initiate where they do.

Earthquake instability models have possible application to earthquake forecasting because the models simulate both preseismic and coseismic changes of fault slip and ground deformation. In the forecast procedure proposed here, repeated measurements of preseismic fault slip and ground deformation constrain the values of model parameters. The early part of the model simulation corresponds to the available field data, and the subsequent part constitutes an estimate of future faulting and ground deformation. In particular, the time, location, and size of unstable faulting are estimates of the pending earthquake parameters. The forecast accuracy depends on the model realism and parameter resolution. The forecast procedure is applied to fault creep and trilateration data measured near Parkfield, California, where at least five magnitude 5.5 to 6 earthquakes have occurred regularly since 1881, the last in 1966. The quasi-static model consists of a flat vertical plane embedded in an elastic half space. Spacially variable fault slip of strike-slip sense is driven by an increasing regional shear stress but is impeded by a relatively strong patch of brittle, strain-softening fault. The field data are consistent with these approximate values of patch parameters: radius of 3 km, patch center 5 km deep and 8 km southeast of the 1966 epicenter, and maximum brittle strength of 26 bars. Fluctuations in the available field data prevent estimating the earthquake time with any more precision than use of the 21±8 year recurrence interval. However, the model may later give a more precise estimate of the earthquake time if the fault slip rate near the inferred patch increases before the earthquake, as predicted by the model.

Seismic moments Mo and local magnitudes ML for earthquakes near Oroville, California imply the linear log seismic moment-local magnitude relation log ⁡ 10 ( M o ) = ( 1.21 ± 0.03 ) M L + ( 17.02 ± 0.07 ) for 17 < log 10 M o < 25. Coda durations τ for short-period, vertical-component seismographs located in the epicentral region are related to local magnitude using two linear log τ-ML segments with point of intersection at ML ≂ 1.5. The rms error is 0.1 to 0.2 units of magnitude. A relation of the form log Mo = a1 + a3 (log τ)2 is sufficient (in the sense that rms error in log10Mo is 0.2 to 0.3 units) to relate τ and Mo for 18 ≦ log10Mo < 22. Coefficients for the above τ-ML and τ-Mo relationships are established for three seismographs of differing response

Quarry blasts provide an excellent source of waves with which to study temporal variations of seismic travel times. Using sources from several active quarries we found no time changes at Gold Hill (GHC), California from 7 months before the 1966 Parkfield mainshock to at least 13 months following the event. GHC is within 0.5 km of the zone of ground breakage associated with the earthquake. This event was one of the largest to occur in central California since 1906. The negative result of our experiment does not rule out the existence of an anomaly prior to the event, rather it emphasizes the difficulty of detecting such anomalies without a fortuitous combination of sources and stations. The routine monitoring of temporal changes in seismic velocity along the San Andreas fault may require not only dense networks of high quality seismic stations, but also sources whose spatial location and origin time can be controlled.

The 25-km-long section of the San Andreas fault near Parkfield, California ruptured in similar magnitude-6 earthquakes in 1881, 1901, 1922, 1934 and 1966. On the basis of a number of lines of seismological evidence, a section of the San Andreas fault, now termed the Parkfield preparation zone, has been identified as the locus of the next Parkfield earthquake1,3. Here we describe coincident changes in surface creep rates and deep seismicity near the Parkfield preparation zone following the 2 May 1983 Coalinga earthquake, and suggest that both respond to the same stimuli. These changes were concentrated near the point of initiation of the magnitude-6 characteristic Parkfield earthquakes, lending credence to the hypothesis that this section of the San Andreas fault is characterized by a unique set of physical properties4–6 which make it ideal for earthquake prediction studies and which may also be useful for identifying hypocentral regions in other areas.

A method is described for the determination of the regions of the parameter space corresponding to stability and instability of the null solution of a restricted system of linear, periodic-coefficient ordinary homogeneous differential equations. The method is applicable to equations which represent the motion of a completely damped mechanical system. For such systems, there can be no periodic or almost-periodic solutions within the region of the parameter space corresponding to stable null solutions. Accordingly, by establishing those parameter values for which almost-periodic solutions are possible, one can determine the boundaries of the regions in the parameter space corresponding to stable solutions. This is accomplished by substituting an almost-periodic solution as the product of a specific periodic function and a Fourier series, obtaining by numerical search those parameter values which guarantee the existence of such a solution by the vanishing of a suitable approximation of a determinant of infinite size. This method is applied to a current problem in space vehicle dynamics, and comparison is made with a numerical implementation of Floquet theory.

Five moderate (magnitude 6) earthquakes with similar features have occurred on the Parkfield section of the San Andreas fault in central California since 1857. The next moderate Parkfield earthquake is expected to occur before 1993. The Parkfield prediction experiment is designed to monitor the details of the final stages of the earthquake preparation process; observations and reports of seismicity and aseismic slip associated with the last moderate Parkfield earthquake in 1966 constitute much of the basis of the design of the experiment.

Moderate-size earthquakes occurred on the Parkfield section of the San Andreas fault in central California in 1881, 1901, 1922, 1934, and in 1966. The earlier Parkfield earthquakes were similar to the 1966 event, leading to the hypothesis of a characteristic Parkfield earthquake with recurring, recognizable source features. A simple recurrence model that explains most of the historic seismicity near Parkfield implies that the next characteristic Parkfield earthquake will occur within a ten year time window centered on 1987–1988. A Parkfield Prediction Experiment, designed to monitor the details of the final stages of the earthquake preparation process is underway. Observations and reports of anomalous seismicity and aseismic slip preceding the last characteristic earthquake in 1966 constitute much of the basis for the design of the Parkfield Prediction Experiment; other design considerations involve testing models of the deformation process leading to failure.

The Morgan Hill, California, earthquake (magnitude 6.1) of 24 April 1984 ruptured a 30-kilometer-long segment of the Calaveras fault zone to the east of San Jose. Although it was recognized in 1980 that an earthquake of magnitude 6 occurred on this segment in 1911 and that a repeat of this event might reasonably be expected, no short-term precursors were noted and so the time of the 1984 earthquake was not predicted. Unilateral rupture propagation toward the south-southeast and an energetic late source of seismic radiation located near the southeast end of the rupture zone contributed to the highly focused pattern of strong motion, including an exceptionally large horizontal acceleration of 1.29g at a site on a dam abutment near the southeast end of the rupture zone.

Longitudinal tension impact tests on nylon tape and Apollo pilot parachute riser construction, determining wave propagation effects

The ratio of the amplitudes of P and S waves from the foreshocks and aftershocks to three recent California earthquakes show a characteristic change at the time of the main events. As this ratio is extremely sensitive to small changes in the orientation of the fault plane, a small systematic change in stress or fault configuration in the source region may be inferred. These results suggest an approach to the recognition of foreshocks based on simple measurements of the amplitudes of seismic waves.

A marked change is observed in P / SV amplitude ratios, measured at station TPC, from foreshocks to aftershocks of the Galway Lake earthquake. This change is interpreted to be the result of a change in fault-plane orientation occurring between foreshocks and aftershocks. The Galway Lake earthquake, M L = 5.2, occurred on June 1, 1975. The first-motion fault-plane solutions for the main shock and most foreshocks and aftershocks indicate chiefly right-lateral strike-slip on NNW-striking planes that dip steeply, 70–90°, to the WSW. The main event was preceded by nine located foreshocks, ranging in magnitude from 1.9 to 3.4, over a period of 12 weeks, starting on March 9, 1975. All of the foreshocks form a tight cluster approximately 1 km in diameter. This cluster includes the main shock. Aftershocks are distributed over a 6-km-long fault zone, but only those that occurred inside the foreshock cluster are used in this study. Seismograms recorded at TPC ( Δ = 61 km ), PEC ( Δ = 93 km ), and CSP ( Δ = 83 km ) are the data used here. The seismograms recorded at TPC show very consistent P / SV amplitude ratios for foreshocks. For aftershocks the P / SV ratios are scattered, but generally quite different from foreshock ratios. Most of the scatter for the aftershocks is confined to the two days following the main shock. Thereafter, however, the P / SV ratios are consistently half as large as for foreshocks. More subtle (and questionable) changes in the P / SV ratios are observed at PEC and CSP. Using theoretical P / SV amplitude ratios, one can reproduce the observations at TPC, PEC and CSP by invoking a 5–12° counterclockwise change in fault strike between foreshocks and aftershocks. This interpretation is not unique, but it fits the data better than invoking, for example, changes in dip or slip angle. First-motion data cannot resolve this small change, but they permit it. Attenuation changes would appear to be ruled out by the fact that changes in the amplitude ratios, P TPC / P PEC and p tpc / p csp , are observed, and these changes accompany the changes in P / SV . Observations for the Galway Lake earthquake are similar to observations for the Oroville, California, earthquake ( M L = 5.7) of August 1, 1975, and the Brianes Hills, California, earthquake ( M L = 4.3) of January 8, 1977 (Lindh et al., Science Vol. 201, pp. 56–59). A change in fault-plane orientation between foreshocks and aftershocks may be understandable in terms of early en-echelon cracking (foreshocks) giving way to shear on the main fault plane (main shock plus aftershocks). Recent laboratory data (Byerlee et al., Tectonophysics, Vol. 44, pp. 161–171) tend to support this view.