The Experts below are selected from a list of 8397 Experts worldwide ranked by ideXlab platform
Egill Hauksson - One of the best experts on this subject based on the ideXlab platform.
-
a structural interpretation of the aftershock cloud of the 1992 mw 7 3 Landers earthquake
Bulletin of the Seismological Society of America, 2003Co-Authors: Jing Liu, Kerry Sieh, Egill HaukssonAbstract:We analyze the spatial relationship of relocated aftershocks to the principal rupture planes of the M w 7.3 1992 Landers mainshock from a structural point of view. We find that the aftershocks constitute primarily a several-kilometer-wide damage zone centered on the mainshock rupture planes. The intensity of damage decreases away from the principal faults. Less than half of the aftershocks occurred within 1 km of the mainshock planes, and perhaps only 5% of the aftershocks are candidates for rerupture of the mainshock faults. Moreover, it seems that aftershocks along the Landers rupture have b -values that correlate well with the complexity of the mainshock rupture. Low b -values occur along segments that are simple, whereas higher b -values correlate with sections that are more complex. Thus, structural complexity appears to correlate with a greater relative abundance of small earthquakes. These observations imply that aftershock populations reflect fault populations in the medium surrounding the principal faults rather than the behavior of the mainshock planes themselves. Online material : Arcview information about the surface rupture of the Landers mainshock.
-
the static stress change triggering model constraints from two southern california aftershock sequences
Journal of Geophysical Research, 1998Co-Authors: Jeanne L Hardebeck, Julie J Nazareth, Egill HaukssonAbstract:Static stress change has been proposed as a mechanism of earthquake triggering. We quantitatively evaluate this model for the apparent triggering of aftershocks by the 1992 M_W 7.3 Landers and 1994 M_W 6.7 Northridge earthquakes. Specifically, we test whether the fraction of aftershocks consistent with static stress change triggering is greater than the fraction of random events which would appear consistent by chance. Although static stress changes appear useful in explaining the triggering of some aftershocks, the model's capability to explain aftershock occurrence varies significantly between sequences. The model works well for Landers aftershocks. Approximately 85% of events between 5 and 75 km distance from the mainshock fault plane are consistent with static stress change triggering, compared to ∼50% of random events. The minimum distance is probably controlled by limitations of the modeling, while the maximum distance may be because static stress changes of <0.01 MPa trigger too few events to be detected. The static stress change triggering model, however, can not explain the first month of the Northridge aftershock sequence significantly better than it explains a set of random events. The difference between the Landers and Northridge sequences may result from differences in fault strength, with static stress changes being a more significant fraction of the failure stress of weak Landers-area faults. Tectonic regime, regional stress levels, and fault strength may need to be incorporated into the static stress change triggering model before it can be used reliably for seismic hazard assessment.
-
state of stress from focal mechanisms before and after the 1992 Landers earthquake sequence
Bulletin of the Seismological Society of America, 1994Co-Authors: Egill HaukssonAbstract:The state of stress in the Eastern California Shear Zone (ECSZ) changed significantly because of the occurrence of the 1992 M_w 6.1 Joshua Tree and the M_W 7.3 Landers earthquakes. To quantify this change, focal mechanisms from the 1975 Galway Lake sequence, the 1979 Homestead Valley sequence, background seismicity from 1981 to 1991, and the 1992 Landers sequence are inverted for the state of stress. In all cases, the intermediate principal stress axis (S2) remained vertical, and changes in the state of stress consisted of variations in the trend of maximum and minimum principal stress axes (S_1 and S_3) and small variations in the value of the relative stress magnitudes (ϕ). In general, the stress state in the ECSZ has S_1 trending east of north and ϕ = 0.43 to 0.65, suggesting that the ECSZ is a moderate stress refractor and the style of faulting is transtensional. South of the Pinto Mountain fault, in the region of the 1992 Joshua Tree earthquake, the stress state determined from the 1981 to 1991 background seismicity changed on 23 April and again on 28 June 1992. In the central zone, S_1 rotated from N14° ± 5°E to N28° ± 5°E on 23 April and back again to N16° ± 5°E on 28 June. Thus, the Landers mainshock in effect recharged some of the shear stress in the region of the M_w 6.1 Joshua Tree earthquake. Comparison of the state of stress before and after 28 June 1992, along the Landers mainshock rupture zone, showed that the mainshock changed the stress orientation. The S1 trend rotated 7° to 20° clockwise and became progressively more fault normal from south to north. Along the Emerson-Camp Rock faults, the variation was so prominent that the focal mechanisms of aftershocks could not be fit by a single deviatoric stress tensor. The complex distribution of P and T axes suggests that most of the uniform component of the applied shear stress along the northern part of the rupture zone was released in the mainshock. The San Bernardino Mountains region of the M_w 6.2 Big Bear earthquake has a distinctively different state of stress, as compared to the Landers region, with S_1 trending N3° ± 5°W. This region did not show any significant change in the state of stress following the 1992 M_w 6.2 Big Bear sequence.
Joan Gomberg - One of the best experts on this subject based on the ideXlab platform.
-
earthquake triggering by seismic waves following the Landers and hector mine earthquakes
Nature, 2001Co-Authors: Joan Gomberg, Paul Bodin, Paul A Reasenberg, Ruth A HarrisAbstract:The proximity and similarity of the 1992, magnitude 7.3 Landers and 1999, magnitude 7.1 Hector Mine earthquakes in California permit testing of earthquake triggering hypotheses not previously possible. The Hector Mine earthquake confirmed inferences that transient, oscillatory ‘dynamic’ deformations radiated as seismic waves can trigger seismicity rate increases, as proposed for the Landers earthquake1,2,3,4,5,6. Here we quantify the spatial and temporal patterns of the seismicity rate changes7. The seismicity rate increase was to the north for the Landers earthquake and primarily to the south for the Hector Mine earthquake. We suggest that rupture directivity results in elevated dynamic deformations north and south of the Landers and Hector Mine faults, respectively, as evident in the asymmetry of the recorded seismic velocity fields. Both dynamic and static stress changes seem important for triggering in the near field with dynamic stress changes dominating at greater distances. Peak seismic velocities recorded for each earthquake suggest the existence of, and place bounds on, dynamic triggering thresholds. These thresholds vary from a few tenths to a few MPa in most places, depend on local conditions, and exceed inferred static thresholds by more than an order of magnitude. At some sites, the onset of triggering was delayed until after the dynamic deformations subsided. Physical mechanisms consistent with all these observations may be similar to those that give rise to liquefaction or cyclic fatigue.
-
stress strain changes and triggered seismicity following the mw 7 3 Landers california earthquake
Journal of Geophysical Research, 1996Co-Authors: Joan GombergAbstract:Calculations of dynamic stresses and strains, constrained by broadband seismograms, are used to investigate their role in generating the remotely triggered seismicity that followed the June 28, 1992 Mw7.3 Landers, California earthquake. I compare straingrams and dynamic Coulomb failure functions calculated for the Landers earthquake at sites that did experience triggered seismicity with those at sites that did not. Bounds on triggering thresholds are obtained from analysis of dynamic strain spectra calculated for the Landers and Mw6.1 Joshua Tree, California earthquakes at various sites, combined with results of static strain investigations by others. I interpret three principal results of this study with those of a companion study by Gomberg and Davis [this issue]. First, the dynamic elastic stress changes themselves cannot explain the spatial distribution of triggered seismicity, particularly the lack of triggered activity along the San Andreas fault system. In addition to the requirement to exceed a Coulomb failure stress level, this result implies the need to invoke and satisfy the requirements of appropriate slip instability theory. Second, results of this study are consistent with the existence of frequency- or rate-dependent stress/strain triggering thresholds, inferred from the companion study and interpreted in terms of earthquake initiation involving a competition of processes, one promoting failure and the other inhibiting it. Such competition is also part of relevant instability theories. Third, the triggering threshold must vary from site to site, suggesting that the potential for triggering strongly depends on site characteristics and response. The lack of triggering along the San Andreas fault system may be correlated with the advanced maturity of its fault gouge zone; the strains from the Landers earthquake were either insufficient to exceed its larger critical slip distance or some other critical failure parameter; or the faults failed stably as aseismic creep events. Variations in the triggering threshold at sites of triggered seismicity may be attributed to variations in gouge zone development and properties. Finally, these interpretations provide ready explanations for the time delays between the Landers earthquake and the triggered events.
-
triggered seismicity and deformation between the Landers california and little skull mountain nevada earthquakes
Bulletin of the Seismological Society of America, 1994Co-Authors: Paul Bodin, Joan GombergAbstract:This article presents evidence for the channeling of strain energy released by the Ms = 7.4 Landers, California, earthquake within the eastern California shear zone (ECSZ). We document an increase in seismicity levels during the 22-hr period starting with the Landers earthquake and culminating 22 hr later with the Ms = 5.4 Little Skull Mountain (LSM), Nevada, earthquake. We evaluate the completeness of regional seismicity catalogs during this period and find that the continuity of post-Landers strain release within the ECSZ is even more pronounced than is evident from the catalog data. We hypothesize that regional-scale connectivity of faults within the ECSZ and LSM region is a critical ingredient in the unprecedented scale and distribution of remotely triggered earthquakes and geodetically manifest strain changes that followed the Landers earthquake. The viability of static strain changes as triggering agents is tested using numerical models. Modeling results illustrate that regional-scale fault connectivity can increase the static strain changes by approximately an order of magnitude at distances of at least 280 km, the distance between the Landers and LSM epicenters. This is possible for models that include both a network of connected faults that slip “sympathetically” and realistic levels of tectonic prestrain. Alternatively, if dynamic strains are a more significant triggering agent than static strains, ECSZ structure may still be important in determining the distribution of triggered seismic and aseismic deformation.
Debi Kilb - One of the best experts on this subject based on the ideXlab platform.
-
a strong correlation between induced peak dynamic coulomb stress change from the 1992 m7 3 Landers california earthquake and the hypocenter of the 1999 m7 1 hector mine california earthquake
Journal of Geophysical Research, 2003Co-Authors: Debi KilbAbstract:The 1992 M7.3 Landers earthquake may have played a role in triggering the 1999 M7.1 1 Hector Mine earthquake as suggested by their close spatial (∼20 km) proximity. Current investigations of triggering by static stress changes produce differing conclusions when small variations in parameter values are employed. Here I test the hypothesis that large-amplitude dynamic stress changes, induced by the Landers rupture, acted to promote the Hector Mine earthquake. I use a flat layer reflectivity method to model the Landers earthquake displacement seismograms. By requiring agreement between the model seismograms and data, I can constrain the Landers main shock parameters and velocity model. A similar reflectivity method is used to compute the evolution of stress changes. I find a strong positive correlation between the Hector Mine hypocenter and regions of large (>4 MPa) dynamic Coulomb stress changes (peak Δσ f (t)) induced by the Landers main shock. A positive correlation is also found with large dynamic normal and shear stress changes. Uncertainties in peak Δσ f (t) (1.3 MPa) are only 28% of the median value (4.6 MPa) determined from an extensive set (160) of model parameters. Therefore the correlation with dynamic stresses is robust to a range of Hector Mine main shock parameters, as well as to variations in the friction and Skempton's coefficients used in the calculations. These results imply dynamic stress changes may be an important part of earthquake trigging, such that large-amplitude stress changes alter the properties of an existing fault in a way that promotes fault failure.
John R Hipp - One of the best experts on this subject based on the ideXlab platform.
-
do fringe banks create fringe neighborhoods examining the spatial relationship between fringe banking and neighborhood crime rates
Justice Quarterly, 2016Co-Authors: Charis E Kubrin, John R HippAbstract:In the aftermath of one of the worst recessions in US history, high unemployment has placed millions of Americans in precarious financial positions. More than ever, Americans are opting out of traditional financial services, relying instead on “fringe lenders” such as check cashers, payday lenders, and pawnshops to manage their finances. Given their tremendous growth and the concern that consumers who are least able to pay for high-cost, high-risk financial products are most likely to use them, fringe lenders have been the subject of controversy and the focus of much research. Largely unknown, however, are the effects of fringe lenders on the communities where they are located. Given their spatial concentration in low-income neighborhoods with greater concentrations of racial and ethnic minorities—areas with typically more crime—of concern is whether fringe lenders themselves are criminogenic. We consider this by examining the impact of several types of fringe lenders on neighborhood crime rates in Los An...
Charis E Kubrin - One of the best experts on this subject based on the ideXlab platform.
-
do fringe banks create fringe neighborhoods examining the spatial relationship between fringe banking and neighborhood crime rates
Justice Quarterly, 2016Co-Authors: Charis E Kubrin, John R HippAbstract:In the aftermath of one of the worst recessions in US history, high unemployment has placed millions of Americans in precarious financial positions. More than ever, Americans are opting out of traditional financial services, relying instead on “fringe lenders” such as check cashers, payday lenders, and pawnshops to manage their finances. Given their tremendous growth and the concern that consumers who are least able to pay for high-cost, high-risk financial products are most likely to use them, fringe lenders have been the subject of controversy and the focus of much research. Largely unknown, however, are the effects of fringe lenders on the communities where they are located. Given their spatial concentration in low-income neighborhoods with greater concentrations of racial and ethnic minorities—areas with typically more crime—of concern is whether fringe lenders themselves are criminogenic. We consider this by examining the impact of several types of fringe lenders on neighborhood crime rates in Los An...
-
Do fringe banks create fringe neighborhoods? Examining the spatial relationship between fringe banking and neighborhood crime rates
eScholarship University of California, 2016Co-Authors: Charis E KubrinAbstract:In the aftermath of one of the worst recessions in US history, high unemployment has placed millions of Americans in precarious financial positions. More than ever, Americans are opting out of traditional financial services, relying instead on “fringe lenders” such as check cashers, payday lenders, and pawnshops to manage their finances. Given their tremendous growth and the concern that consumers who are least able to pay for high-cost, high-risk financial products are most likely to use them, fringe lenders have been the subject of controversy and the focus of much research. Largely unknown, however, are the effects of fringe lenders on the communities where they are located. Given their spatial concentration in low-income neighborhoods with greater concentrations of racial and ethnic minorities—areas with typically more crime—of concern is whether fringe lenders themselves are criminogenic. We consider this by examining the impact of several types of fringe lenders on neighborhood crime rates in Los Angeles. Our findings reveal that the presence of fringe banks on a block is related to higher crime levels, even after controlling for a range of factors known to be associated with crime rates. The presence of a fringe bank also impacts crime, particularly robbery, on adjacent blocks. Whereas we find that pawnshops have little impact on crime levels, payday lenders and check cashers have a much stronger impact. Finally, we discover there are moderating effects, as the fringe lender–crime relationship is considerably reduced if the lender is located in a higher population density area
