Tremor patches in Cascadia revealed by seismic array analysis

Abstract

Episodic tremor and slip (ETS) events in Cascadia have recently been observed, illuminating the general area that radiates seismic energy in the form of non‐volcanic tremor (NVT). However, the picture of the ETS zone remains fuzzy because of difficulties in tremor detection and location. To observe the intimate details of tremor, we deployed a dense 84‐element small‐aperture seismic array on the Olympic Peninsula, Washington, above the tremor migration path. It recorded the main ETS event in May 2008, as well as a weaker tremor episode two months earlier. Using a beamforming technique, we are able to capture and track tremor activity with an unprecedented resolution from southern Puget Sound to the Strait of Juan de Fuca. The array technique reveals up to four times more duration of tremor compared to the conventional envelope cross‐correlation method. Our findings suggest that NVT is not uniformly distributed on the subduction interface, and unveils several distinct patches that release much of the tremor moment. The patches appear to be devoid of ordinary earthquakes, and may indicate the heterogeneity in fault strength that affects the modes of stress release within the ETS zone.

Complexity of the deep San Andreas Fault zone defined by cascading tremor

“…The same concept has been suggested as a possible mechanism for propagating tremor produced by rerupture of a homogeneous fault 21,22 . However, because the same fault patches consistently generate the strongest tremor 15,28 , fault zone heterogeneity (of some type) seems to play an essential role in tremor generation. After the initial rupture, subsequent ruptures are likely to nucleate at stress concentrations near the fringe of the original rupture and expand the overall slip zone, into the adjacent area that has been stressed but not yet ruptured.…”

Characteristics and interactions between non-volcanic tremor and related slow earthquakes in the Nankai subduction zone, southwest Japan

“…If tremor is related to the underplating process, tremor is expected to be distributed in the thickening direction. A dense seismic array (e.g., Ghosh et al, 2009a) is a powerful observation tool for improving the spatial resolution of tremor. Determination of the three-dimensional relative locations of tremor, VLF earthquakes, and short-term SSEs will resolve the mutual relationships of each constituent member of coupled slow earthquake phenomena.…”

Antioxidant and metal chelating activities of Lagenaria siceraria (Molina) Standl peel, pulp and aerial parts in relation to their total phenol and flavonoid content

“…It cures pain, ulcers and fever and used for pectoral cough, asthma and other bronchial disorders especially syrup prepared from the tender fruits. 7 Some of the reported activities are Hypolipidemic and antihyperlipidemic effects, 8 Diuretic activity, 9 Cardioprotective effect, 10,11 Cytotoxic activity, 12 Antioxidant activity, [13][14][15][16] Antimicrobial activity, 17 Lipid-lowering and antioxidant activity, 18 hepatoprotective activity, 19 antinociceptive and antioxidant from root, 20 antithrombotic potential of the fruits.…”