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Tectonic tremor has been explained as a swarm of low‐frequency earthquakes (LFEs), which are located on a narrow fault at the plate boundary. However, due to the lack of clear impulsive phases in the tremor signal, it is difficult to determine the depth of the tremor source with great precision. The thickness of the tremor region is also not well constrained. The tremor may be located on a narrow fault as the LFEs appear to be, or distributed over a few kilometers wide low shear‐wave velocity layer in the upper oceanic crust, which is thought to be a region with high pore‐fluid pressure. Lag times of peaks in the cross‐correlation of the horizontal and vertical components of tremor seismograms, recorded by small‐aperture arrays in the Olympic Peninsula, Washington, are interpreted to be S minus P times. Tremor depths are estimated from these S minus P times using epicenters from a previous study computed with a multibeam backprojection method. The tremor is located close to the plate boundary in a region no more than 2–3 km thick and is very close to the depths of LFEs. The tremor is distributed over a wider depth range than the LFEs. However, due to the uncertainty on the depth, it is difficult to conclude whether the source of the tremor is located at the top of the subducting oceanic crust, in the lower continental crust just above the plate boundary, or in a narrow zone at the plate boundary. Plain Language Summary: Tectonic tremor is a long, low amplitude seismic signal, with emergent onsets, and an absence of clear impulsive phases. It has been explained as a swarm of low‐frequency earthquakes (LFEs), which are located on a narrow fault at the plate boundary. It is therefore assumed that the source of the tectonic tremor is located close to the plate boundary. However, due to the lack of clear impulsive phases in the tremor signal, it is difficult to determine the depth of the tremor source and the distance of the source to the plate interface with great precision. The thickness of the tremor region is not well constrained either. The tremor may be located on a narrow fault like the LFEs, or distributed through a few kilometers wide low shear‐wave velocity layer in the upper oceanic crust, which is thought to be a region with high pore‐fluid pressure. In this paper, we show that the tremor is located close to the plate boundary in a region no more than 2–3 km thick and is very close to the depths of LFEs. Knowing the depth of the tremor source will help understand the mechanism that produces the tremor. Key Points: We use seismic data from small‐aperture arrays in the Olympic Peninsula, and tremor epicenters determined by a previous studyWe compute the depth of the tremor from S minus P times determined from stacking horizontal‐to‐vertical cross‐correlations of seismic dataTremor is located close to the plate boundary in a region no more than 2–3 km thick [ABSTRACT FROM AUTHOR]

Upper‐plate faulting in the Olympic Peninsula of Washington State results from relative motion of crustal blocks within the Cascadia forearc and earthquake cycle processes along the Cascadia subduction zone. We reconstruct fault slip rates since ∼14 ka on the Sadie Creek fault (SCF), north of the Olympic Mountains, using airborne lidar and field mapping of surficial deposits and landforms and optically stimulated luminescence and radiocarbon dating. The SCF is a ≥14 km‐long northwest‐striking, subvertical, dextral strike‐slip fault with a subordinate dip‐slip component. Laterally, offset debris flow channels cut into Late‐Pleistocene and younger surfaces show dextral slip of 4.0–24.5 m and dip slip of 0.7–6.5 m. Re‐evaluation of fault slip on the adjacent Lake Creek Boundary Creek fault (LCBCF) shows similar dextral (4.5–29.7 m) and dip slip (0.8–4.6 m). A deglacial age of 14 ka paired with the largest—and presumably oldest—slip measurements produce a minimum dextral slip rate of 1.3–2.3 mm/yr and dip‐slip rate of 0.05–0.5 mm/yr. Similarities in geometry, kinematics, slip rate, and earthquake timing between the SCF and LCBCF suggest these faults represent one continuous geologic structure, the North Olympic fault zone. Geodetically constrained boundary element method models considering the effects of coseismic subduction zone stresses on upper plate structures produce comparable kinematics to those measured on the SCF and LCBCF, suggesting that the North Olympic fault zone acts as the main strain‐accommodating structure in the northern Olympic Peninsula and may be modulated by stress transferred from subduction zone earthquakes. Key Points: The Sadie Creek fault is characterized by a minimum post‐14 ka slip rate of 1.3–2.3 mm/yrSimilarities in slip between the Sadie Creek fault and Lake Creek Boundary Creek fault suggest these faults represent one continuous structure, the North Olympic fault zoneComparison of measured and modeled slip rates suggest crustal faults may be modulated by stress transferred from subduction zone earthquakes [ABSTRACT FROM AUTHOR]

The article offers information on the efforts of seismologists at the University of Washington in Seattle, Washington to learn and interpret the small earthquakes nearby the Olympic Peninsula which can help researchers monitor and prepare for a big earthquake. It says that a seismic sensor was planted in the peninsula's mountain ground to locate the source of vibrations and to understand the physical process of the activity. It also notes that tremors is originally from below ground areas that store up energy which cause future large earthquakes. It adds that one of the researcher's goal is to determine what conditions can produce tremors and future earthquakes.