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Concept: 1906 San Francisco earthquake


Abnormal increases in radon ((222)Rn, half-life = 3.82 days) activity have occasionally been observed in underground environments before major earthquakes. However, (222)Rn alone could not be used to forecast earthquakes since it can also be increased due to diffusive inputs over its lifetime. Here, we show that a very short-lived isotope, thoron ((220)Rn, half-life = 55.6 s; mean life = 80 s), in a cave can record earthquake signals without interference from other environmental effects. We monitored (220)Rn together with (222)Rn in air of a limestone-cave in Korea for one year. Unusually large (220)Rn peaks were observed only in February 2011, preceding the 2011 M9.0 Tohoku-Oki Earthquake, Japan, while large (222)Rn peaks were observed in both February 2011 and the summer. Based on our analyses, we suggest that the anomalous peaks of (222)Rn and (220)Rn activities observed in February were precursory signals related to the Tohoku-Oki Earthquake. Thus, the (220)Rn-(222)Rn combined isotope pair method can present new opportunities for earthquake forecasting if the technique is extensively employed in earthquake monitoring networks around the world.

Concepts: Future, Japan, Forecasting, Earthquake, Earthquake prediction, Aftershock, 1906 San Francisco earthquake, Earthquakes


The deep extension of the San Andreas Fault is believed to be creeping, but the recent observations of tectonic tremors from these depths indicate a complex deformation style. In particular, an isolated tremor source near Parkfield has been producing a sequence of low-frequency earthquakes that indicates an uncommon mechanism of stress accumulation and release. The tremor pattern regularly oscillated between three and six days from mid-2003 until it was disrupted by the 2004 magnitude 6.0 Parkfield earthquake. After that event, the tremor source ruptured only about every three days, but over the next two years it gradually returned to its initial alternating recurrence pattern. The mechanism that drives this recurrence pattern is unknown. Here we use physics-based models to show that the same tremor asperity-the region from which the low-frequency earthquakes radiate-can regularly slip in slow and fast ruptures, naturally resulting in recurrence intervals alternating between three and six days. This unusual slip behaviour occurs when the tremor asperity size is close to the critical nucleation size of earthquakes. We also show that changes in pore pressure following the Parkfield earthquake can explain the sudden change and gradual recovery of the recurrence intervals. Our findings suggest a framework for fault deformation in which the same asperity can release tectonic stress through both slow and fast ruptures.

Concepts: Plate tectonics, Metaphysics, Earthquake, Fault, 1906 San Francisco earthquake, San Andreas Fault, Parkfield earthquake, Parkfield, California


Do adversarial environmental conditions create social cohesion? We provide new answers to this question by exploiting spatial and temporal variation in exposure to earthquakes across Chile. Using a variety of methods and controlling for a number of socio-economic variables, we find that exposure to earthquakes has a positive effect on several indicators of social cohesion. Social cohesion increases after a big earthquake and slowly erodes in periods where environmental conditions are less adverse. Our results contribute to the current debate on whether and how environmental conditions shape formal and informal institutions.

Concepts: Sociology, Environmental science, Society, 1906 San Francisco earthquake, Pacific Ring of Fire


Why many major strike-slip faults known to have had large earthquakes are silent in the interseismic period is a long-standing enigma. One would expect small earthquakes to occur at least at the bottom of the seismogenic zone, where deeper aseismic deformation concentrates loading. We suggest that the absence of such concentrated microseismicity indicates deep rupture past the seismogenic zone in previous large earthquakes. We support this conclusion with numerical simulations of fault behavior and observations of recent major events. Our modeling implies that the 1857 Fort Tejon earthquake on the San Andreas Fault in Southern California penetrated below the seismogenic zone by at least 3 to 5 kilometers. Our findings suggest that such deeper ruptures may occur on other major fault segments, potentially increasing the associated seismic hazard.

Concepts: 2000s music groups, California, Earthquake, Southern California, Fault, 1906 San Francisco earthquake, San Andreas Fault, Fort Tejon


The scarcity of long geological records of major earthquakes, on different types of faults, makes testing hypotheses of regular versus random or clustered earthquake recurrence behavior difficult. We provide a fault-proximal major earthquake record spanning 8000 years on the strike-slip Alpine Fault in New Zealand. Cyclic stratigraphy at Hokuri Creek suggests that the fault ruptured to the surface 24 times, and event ages yield a 0.33 coefficient of variation in recurrence interval. We associate this near-regular earthquake recurrence with a geometrically simple strike-slip fault, with high slip rate, accommodating a high proportion of plate boundary motion that works in isolation from other faults. We propose that it is valid to apply time-dependent earthquake recurrence models for seismic hazard estimation to similar faults worldwide.

Concepts: Plate tectonics, New Zealand, Geology, Earthquake, Seismology, Subduction, Fault, 1906 San Francisco earthquake


The objectives of this study were to compare prevalence rates of different pathologies, ambulance system and emergency department management times, and patient survival and hazard ratios for codes 2 and 3 in two hub hospitals in Modena in the 36-month period across the stages of two major earthquakes in short sequence in Northern Italy in 2012.

Concepts: Hospital, Italy, Veneto, Southern Italy, Northern Italy, Seismology, Emergency, 1906 San Francisco earthquake


We test here the risk communication proposition that explicit expert acknowledgment of uncertainty in risk estimates can enhance trust and other reactions. We manipulated such a scientific uncertainty message, accompanied by probabilities (20%, 70%, implicit [“will occur”] 100%) and time periods (10 or 30 years) in major (≥magnitude 8) earthquake risk estimates to test potential effects on residents potentially affected by seismic activity on the San Andreas fault in the San Francisco Bay Area (n = 750). The uncertainty acknowledgment increased belief that these specific experts were more honest and open, and led to statistically (but not substantively) significant increases in trust in seismic experts generally only for the 20% probability (vs. certainty) and shorter versus longer time period. The acknowledgment did not change judged risk, preparedness intentions, or mitigation policy support. Probability effects independent of the explicit admission of expert uncertainty were also insignificant except for judged risk, which rose or fell slightly depending upon the measure of judged risk used. Overall, both qualitative expressions of uncertainty and quantitative probabilities had limited effects on public reaction. These results imply that both theoretical arguments for positive effects, and practitioners' potential concerns for negative effects, of uncertainty expression may have been overblown. There may be good reasons to still acknowledge experts' uncertainties, but those merit separate justification and their own empirical tests.

Concepts: Risk, Decision theory, California, Uncertainty, San Francisco Bay Area, San Francisco, 1906 San Francisco earthquake, San Andreas Fault


Millions of children were exposed to major earthquake in China, with serious psychological and developmental consequences. To obtain accurate rate of post-disaster related disorder and identify predictors may help inform post-disaster rescue and rehabilitation efforts. The present longitudinal study explored correlations of demographic and socioeconomic characteristics of juvenile survivors of the Ya'an and Wenchuan earthquakes in China with their trajectories of post-disaster related disorder.

Concepts: Time, Sociology, Mental disorder, Earthquake, Richter magnitude scale, Moment magnitude scale, 2008 Sichuan earthquake, 1906 San Francisco earthquake


Studying small repeating earthquakes enables better understanding of fault physics and characterization of fault friction properties. Some of the nearby repeating sequences appear to interact, such as the ‘San Francisco’ and ‘Los Angeles’ repeaters on the creeping section of the San Andreas Fault. It is typically assumed that such interactions are induced by static stress changes due to coseismic slip. Here we present a study of the interaction of repeating earthquakes in the framework of rate-and-state fault models using state-of-the-art simulation methods that reproduce both realistic seismic events and long-term earthquake sequences. Our simulations enable comparison among several types of stress transfer that occur between the repeating events. Our major finding is that postseismic creep dominates the interaction, with earthquake triggering occurring at distances much larger than typically assumed. Our results open a possibility of using interaction of repeating sequences to constrain friction properties of creeping segments.

Concepts: California, Earthquake, Los Angeles, Seismology, San Francisco Bay Area, San Francisco, 1906 San Francisco earthquake, San Andreas Fault


Using the Japan Meteorological Agency earthquake catalog, we investigate the seismicity variations before major earthquakes in the Japanese region. We apply natural time, the new time frame, for calculating the fluctuations, termed β, of a certain parameter of seismicity, termed κ1. In an earlier study, we found that β calculated for the entire Japanese region showed a minimum a few months before the shallow major earthquakes (magnitude larger than 7.6) that occurred in the region during the period from 1 January 1984 to 11 March 2011. In this study, by dividing the Japanese region into small areas, we carry out the β calculation on them. It was found that some small areas show β minimum almost simultaneously with the large area and such small areas clustered within a few hundred kilometers from the actual epicenter of the related main shocks. These results suggest that the present approach may help estimation of the epicentral location of forthcoming major earthquakes.

Concepts: Time, Japan, Earthquake, Great Hanshin earthquake, Seismic wave, Richter magnitude scale, Epicenter, 1906 San Francisco earthquake