Chastity Aiken

Bio: Chastity Aiken is an academic researcher from IFREMER. The author has contributed to research in topics: Fault (geology) & Remotely triggered earthquakes. The author has an hindex of 12, co-authored 33 publications receiving 643 citations. Previous affiliations of Chastity Aiken include University of Texas at Austin & Georgia Institute of Technology.

Triggered creep as a possible mechanism for delayed dynamic triggering of tremor and earthquakes

Abstract: The passage of radiating seismic waves generates transient stresses in the Earth’s crust that can trigger slip on faults far away from the original earthquake source. The triggered fault slip is detectable in the form of earthquakes 1‐3 and seismic tremor 4‐7 . However, the significance of these triggered events remains controversial 8,9 , in part because they often occur with some delay, long after the triggering stress has passed. Here we scrutinize the location and timing of tremor on the San Andreas fault between 2001 and 2010 in relation to distant earthquakes. We observe tremor on the San Andreas fault that is initiated by passing seismic waves, yet migrates along the fault at a much slower velocity than the radiating seismic waves. We suggest that the migrating tremor records triggered slow slip of the San Andreas fault as a propagating creep event. We find that the triggered tremor and fault creep can be initiated by distant earthquakes as small as magnitude 5.4 and can persist for several days after the seismic waves have passed. Our observations of prolonged tremor activity provide a clear example of the delayed dynamic triggering of seismic events. Fault creep has been shown to trigger earthquakes 10‐12 , and we therefore suggest that the dynamic

A Global Search for Triggered Tremor Following the 2011 Mw 9.0 Tohoku Earthquake

Abstract: The 2011 M w 9.0 Tohoku, Japan, earthquake triggered deep tectonic tremor and shallow microearthquakes in numerous places worldwide. Here, we conduct a systematic survey of triggered tremor in regions where ambient or triggered tremor has been previously identified. Tremor was triggered in the following regions: south‐central Alaska, the Aleutian Arc, Shikoku in southwest Japan, the North Island of New Zealand, southern Oregon, the Parkfield–Cholame section of the San Andreas fault in central California, the San Jacinto fault in southern California, Taiwan, and Vancouver Island. We find no evidence of triggered tremor in the Calaveras fault in northern California. One of the most important factors in controlling the triggering potential is the amplitude of the surface waves. Data examined in this study suggest that the threshold amplitude for triggering tremor is ∼0.1 cm/s, which is equivalent to a dynamic stress threshold of ∼10 kilopascals. The incidence angles of the teleseismic surface waves also affect the triggering potentials of Love and Rayleigh waves. The results of this study confirm that both Love and Rayleigh waves contribute to triggering tremor in many regions. In regions where both ambient and triggered tremor are known to occur, tremor triggered by the Tohoku event generally occurred at similar locations with previously identified ambient and/or triggered tremor, further supporting the notion that although the driving forces of triggered and ambient tremor differ, they share similar mechanisms. We find a positive relationship between the amplitudes of the triggering waves and those of the triggered tremor, which is consistent with the prediction of the clock‐advance model. Online Material: Table of measured parameters and other information related to triggering/nontriggering information, and figures of observed seismograms.

Dynamic triggering of microearthquakes in three geothermal/volcanic regions of California

Abstract: Geothermal/volcanic regions are most susceptible to local earthquake triggering by regional and remote earthquakes. Transient stresses caused by surface waves of these earthquakes can activate critically stressed faults. Though earthquakes can be triggered in geothermal/volcanic regions, it is less understood how these regions differ in their triggering responses to distant earthquakes. We conduct a systematic survey of local earthquakes triggered by distant earthquakes in three geothermal/volcanic regions of California: Long Valley Caldera, Coso Geothermal Field, and Geysers Geothermal Field. We examine waveforms of distant earthquakes with magnitudes ≥ 5.5 occurring between 2000 and 2012 and compute β statistics to confirm the significance of our findings. We find that Long Valley, Coso, and Geysers vary in triggering frequency—2.0%, 3.8%, and 6.8% in the 12 year period, respectively—and when compared to the triggering of deep tectonic tremors along the Parkfield-Cholame section of San Andreas Fault (9.2% in the 12 year period). Stress triggering thresholds vary among the regions with Long Valley having the highest of ~5 kPa and ~1 kPa for the other regions. Because dynamic stresses from distant earthquakes are similar in these three regions, the varying triggering behavior likely reflects faults having a tendency to be at or near failure. This is compatible with Geysers having a higher a value in the Gutenberg-Richter relationship and higher geothermal productivity than the other two regions. The observation of more frequent triggering of tremor than microearthquakes is consistent with recent laboratory studies on increasing triggerability with lower effective stress.

Tremors along the Queen Charlotte Margin triggered by large teleseismic earthquakes

Abstract: [1] We conduct a systematic search of tectonic tremors along the Queen Charlotte Margin (QCM) in western Canada triggered by distant earthquakes. We identify triggered tremor as non-impulsive, high-frequency signals coherent among several stations and coincident with passing surface waves. So far, the 2002 Mw7.9 Denali Fault, the 2004 Mw9.2 Sumatra, and the 2011 Mw9.1 Tohoku-Oki earthquakes have triggered clear tremor in this region. The 2010 Mw8.8 Maule, Chile and the 2012 Mw8.6 Sumatra earthquakes may have triggered, but tremors in these two cases did not meet all of our criteria. The triggered tremors are mostly located east of the Queen Charlotte Fault in the southern portion of Haida Gwaii, near the epicenter of the 28 October 2012 Mw7.7 earthquake. Similar to the observations in other regions, the triggered tremors were initiated by the Love waves and continued during the subsequent Rayleigh waves. Tremor bursts correlate with both the particle velocity and displacement of the Love waves, indicating they are triggered at either low-angle thrust or vertical strike-slip faults. In addition, we find that the triggering potential for the QCM is controlled by a combination of amplitude, period, and incident angles.

Remotely triggered microearthquakes and tremor in central California following the 2010 Mw 8.8 Chile earthquake

Abstract: [1] We examine remotely triggered microearthquakes and tectonic tremor in central California following the 2010 Mw 88 Chile earthquake Several microearthquakes near the Coso Geothermal Field were apparently triggered, with the largest earthquake (Ml 35) occurring during the large-amplitude Love surface waves The Chile mainshock also triggered numerous tremor bursts near the Parkfield-Cholame section of the San Andreas Fault (SAF) The locally triggered tremor bursts are partially masked at lower frequencies by the regionally triggered earthquake signals from Coso, but can be identified by applying high-pass or matched filters Both triggered tremor along the SAF and the Ml 35 earthquake in Coso are consistent with frictional failure at different depths on critically-stressed faults under the Coulomb failure criteria The triggered tremor, however, appears to be more phase-correlated with the surface waves than the triggered earthquakes, likely reflecting differences in constitutive properties between the brittle, seismogenic crust and the underlying lower crust

Connecting slow earthquakes to huge earthquakes

Abstract: Slow earthquakes are characterized by a wide spectrum of fault slip behaviors and seismic radiation patterns that differ from those of traditional earthquakes. However, slow earthquakes and huge megathrust earthquakes can have common slip mechanisms and are located in neighboring regions of the seismogenic zone. The frequent occurrence of slow earthquakes may help to reveal the physics underlying megathrust events as useful analogs. Slow earthquakes may function as stress meters because of their high sensitivity to stress changes in the seismogenic zone. Episodic stress transfer to megathrust source faults leads to an increased probability of triggering huge earthquakes if the adjacent locked region is critically loaded. Careful and precise monitoring of slow earthquakes may provide new information on the likelihood of impending huge earthquakes.

Computational Thinking 計算論的思考

Abstract: It represents a universally applicable attitude and skill set everyone, not just computer scientists, would be eager to learn and use.

Global warming and winter weather.

Abstract: In mid-January, a lobe of the polar vortex sagged southward over the central and eastern United States. All-time low temperature records for the calendar date were set at O'Hare Airport in Chicago [−16°F (−27°C), 6 January], at Central Park in New York [4°F (−15.6°C), 7 January], and at

Ancient low–molecular-weight organic acids in permafrost fuel rapid carbon dioxide production upon thaw

Abstract: Northern permafrost soils store a vast reservoir of carbon, nearly twice that of the present atmosphere. Current and projected climate warming threatens widespread thaw of these frozen, organic carbon (OC)-rich soils. Upon thaw, mobilized permafrost OC in dissolved and particulate forms can enter streams and rivers, which are important processors of OC and conduits for carbon dioxide (CO2) to the atmosphere. Here, we demonstrate that ancient dissolved organic carbon (DOC) leached from 35,800 y B.P. permafrost soils is rapidly mineralized to CO2. During 200-h experiments in a novel high–temporal-resolution bioreactor, DOC concentration decreased by an average of 53%, fueling a more than sevenfold increase in dissolved inorganic carbon (DIC) concentration. Eighty-seven percent of the DOC loss to microbial uptake was derived from the low–molecular-weight (LMW) organic acids acetate and butyrate. To our knowledge, our study is the first to directly quantify high CO2 production rates from permafrost-derived LMW DOC mineralization. The observed DOC loss rates are among the highest reported for permafrost carbon and demonstrate the potential importance of LMW DOC in driving the rapid metabolism of Pleistocene-age permafrost carbon upon thaw and the outgassing of CO2 to the atmosphere by soils and nearby inland waters.