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Faults & earthquakes

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At least 55 records · Page 3Linked to original sources

USGS2024

Rupture jumping and seismic complexity in models of earthquake cycles for fault stepovers with off‐fault plasticity

Fault stepovers are prime examples of geometric complexity in natural fault zones that may affect seismic hazard by determining whether an earthquake rupture continues propagating or abruptly stops. However, the long‐term pattern of seismicity near‐fault stepovers and underlying mechanisms of rupture jumping in the context of earthquake cycles are rarely studied. Leveraging a hybrid numerical scheme combining the finite element and the spectral boundary integral methods, FEBE, we carry out fully dynamic simulations of sequences of earthquakes and aseismic slip for both compressive and tensile stepovers with off‐fault plasticity. We consider a rate‐and‐state friction law for the fault friction and pressure‐sensitive Drucker–Prager plasticity for the off‐fault bulk response. We observe that the accumulation of plastic deformation, an indication of off‐fault damage, is significantly different in the two cases, with more plastic deformation projected in the overlapping region for the tensile stepover. The seismic pattern for a tensile stepover is more complex than for a compressive stepover, and incorporating plasticity also increases complexity, relative to the elastic case. A tensile stepover with off‐fault plasticity shows rupture segmentation, temporal clustering, and frequent rupture jumping from one fault to another. These results shed light on possible mechanisms of rupture jumping in fault stepovers as well as the long‐term evolution of the fault zone.

Bulletin of the Seismological Șociety of America↗

USGS2013

The Mw 5.8 Mineral, Virginia, earthquake of August 2011 and aftershock sequence: constraints on earthquake source parameters and fault geometry

The M w 5.8 earthquake of 23 August 2011 (17:51:04 UTC) (moment, M0 5.7×10 17 N·m) occurred near Mineral, Virginia, within the central Virginia seismic zone and was felt by more people than any other earthquake in United States history. The U.S. Geological Survey (USGS) received 148,638 felt reports from 31 states and 4 Canadian provinces. The USGS PAGER system estimates as many as 120,000 people were exposed to shaking intensity levels of IV and greater, with approximately 10,000 exposed to shaking as high as intensity VIII. Both regional and teleseismic moment tensor solutions characterize the earthquake as a northeast‐striking reverse fault that nucleated at a depth of approximately 7±2 km. The distribution of reported macroseismic intensities is roughly ten times the area of a similarly sized earthquake in the western United States (Horton and Williams, 2012). Near‐source and far‐field damage reports, which extend as far away as Washington, D.C., (135 km away) and Baltimore, Maryland, (200 km away) are consistent with an earthquake of this size and depth in the eastern United States (EUS). Within the first few days following the earthquake, several government and academic institutions installed 36 portable seismograph stations in the epicentral region, making this among the best‐recorded aftershock sequences in the EUS. Based on modeling of these data, we provide a detailed description of the source parameters of the mainshock and analysis of the subsequent aftershock sequence for defining the fault geometry, area of rupture, and observations of the aftershock sequence magnitude–frequency and temporal distribution. The observed slope of the magnitude–frequency curve or b‐value for the aftershock sequence is consistent with previous EUS studies (b=0.75), suggesting that most of the accumulated strain was released by the mainshock. The aftershocks define a rupture that extends between approximately 2–8 km in depth and 8–10 km along the strike of the fault plane. Best‐fit modeling of the geometry of the aftershock sequence defines a rupture plane that strikes N36°E and dips to the east‐southeast at 49.5°. Moment tensor solutions of the mainshock and larger aftershocks are consistent with the distribution of aftershock locations, both indicating reverse slip along a northeast–southwest striking southeast‐dipping fault plane.

Virginia↗

USGS1978

Local magnetic field measurements, fault creep observations and local earthquakes on the San Andreas fault

Simultaneous records of local variations in magnetic field, fault creep and the occurrence times of local earthquakes have been obtained for the period early 1974 through mid-1977 along the San Andreas fault between the most southern extent of the 1906 earthquake fault break and the most northern extent of the 1857 break. The data utilized are primarily from stations located near the two ends of this section of the fault where strains accumulation is expected. The magnetic data show that local magnetic field variations up to 1.8 gammas with durations of a few minutes to several months have occurred. The creep data indicate both episodic events and changes in creep rate of up to 10 mm/yr lasting for six months or more. No clear magnetic transients or offsets are evident either simultaneous with or preceding the occurrence times of the episodic creep events by up to a day or so. Although some patterns of creep onset times at adjacent stations appear to correspond to some periods of longer term change in local magnetic field, these changes do not always occur and other groups of creep events have no corresponding changes in local magnetic field. Earthquakes with magnitudes less than 4.0 do not appear to correspond in time to local changes in magnetic field greater than 0.8 gamma or variations in the creep rate. In order to explain the observations presented in this study, it appears necessary to allow for a substantial amount of deep aseismic slip without any obvious attendant changes in the time distribution or size of the local earthquakes. Changes in stress related to the surface expression of aseismic slip on the San Andreas fault can be estimated from dislocation models fit to these data and to observations of simultaneous strains and tilts at points near the fault. These stress values are on average less than one bar near the surface but are probably more than 10 bars in localized regions at depths of a kilometer or so.

California↗

USGS2015

2014 M=6.0 South Napa earthquake triggered widespread aftershocks and stressed several major faults and exotic fault clusters

The strongest San Francisco Bay area earthquake since the 1989 Mw 7.0 Loma Prieta shock struck near Napa on 24 August 2014. Field mapping (Dawson et al., 2014; Earthquake Engineering Research Institute [EERI], 2014; Brocher et al., 2015) and seismic and geodetic source inversions (Barnhart et al., 2015; Dreger et al., 2015; Wei et al., 2015) indicate that a 15-km-long northwest-trending section of the West Napa Valley fault ruptured in the earthquake. Remarkably, it was the first indisputable surface rupture in the Bay area since 1906. The Napa event, along with other smaller earthquakes such as the 1980 Mw 5.8 Livermore and 1984 Mw 6.2 Morgan Hill events on the Calaveras and Hayward faults over the past 3–4 decades, may indicate that the Bay area region is emerging from the stress shadow of the 1906 Mw 7.8 San Francisco earthquake (Harris and Simpson, 1998; Pollitz et al., 2004). Since 1979, there has been a 140% increase in the rate of Mw≥4.1 shocks (Fig. 1) in the broader Bay area, with most concentrated in a corridor extending north from the 1989 Loma Prieta aftershock zone through the Calaveras, Greenville, Green Valley, Napa, and Rodgers Creek faults east of the San Francisco Bay (Fig. 1a). This corridor roughly coincides with the 1906 stress shadow that is being eroded away by more than a century of stress reaccumulation. The Napa event, as well as the surrounding faults on which we calculate the resulting hazard increases, all lie within this zone.

California↗

USGS2007

Relatively simple through-going fault planes at large-earthquake depth may be concealed by the surface complexity of strike-slip faults

At the surface, strike-slip fault stepovers, including abrupt fault bends, are typically regions of complex, often disconnected faults. This complexity has traditionally led geologists studying the hazard of active faults to consider such stepovers as important fault segment boundaries, and to give lower weight to earthquake scenarios that involve rupture through the stepover zone. However, recent geological and geophysical studies of several stepover zones along the San Andreas fault system in California have revealed that the complex nature of the fault zone at the surface masks a much simpler and direct connection at depths associated with large earthquakes (greater than 5 km). In turn, the simplicity of the connection suggests that a stepover zone would provide less of an impediment to through-going rupture in a large earthquake, so that the role of stepovers as segment boundaries has probably been overemphasized. However, counter-examples of fault complexity at depth associated with surface stepovers are known, so the role of stepovers in fault rupture behaviour must be carefully established in each case.

California↗

USGS2016

Fluid-faulting evolution in high definition: Connecting fault structure and frequency-magnitude variations during the 2014 Long Valley Caldera, California earthquake swarm

An extended earthquake swarm occurred beneath southeastern Long Valley Caldera between May and November 2014, culminating in three magnitude 3.5 earthquakes and 1145 cataloged events on 26 September alone. The swarm produced the most prolific seismicity in the caldera since a major unrest episode in 1997-1998. To gain insight into the physics controlling swarm evolution, we used large-scale cross-correlation between waveforms of cataloged earthquakes and continuous data, producing precise locations for 8494 events, more than 2.5 times the routine catalog. We also estimated magnitudes for 18,634 events (~5.5 times the routine catalog), using a principal component fit to measure waveform amplitudes relative to cataloged events. This expanded and relocated catalog reveals multiple episodes of pronounced hypocenter expansion and migration on a collection of neighboring faults. Given the rapid migration and alignment of hypocenters on narrow faults, we infer that activity was initiated and sustained by an evolving fluid pressure transient with a low-viscosity fluid, likely composed primarily of water and CO 2 exsolved from underlying magma. Although both updip and downdip migration were observed within the swarm, downdip activity ceased shortly after activation, while updip activity persisted for weeks at moderate levels. Strongly migrating, single-fault episodes within the larger swarm exhibited a higher proportion of larger earthquakes (lower Gutenberg-Richter b value), which may have been facilitated by fluid pressure confined in two dimensions within the fault zone. In contrast, the later swarm activity occurred on an increasingly diffuse collection of smaller faults, with a much higher b value.

California↗

USGS2004

Geophysical investigation of the Denali fault and Alaska Range orogen within the aftershock zone of the October–November 2002, M = 7.9 Denali fault earthquake

The aftershock zone of the 3 November 2002, M = 7.9 earthquake that ruptured along the right-slip Denali fault in south-central Alaska has been investigated by using gravity and magnetic, magnetotelluric, and deep-crustal, seismic reflection data as well as outcrop geology and earthquake seismology. Strong seismic reflections from within the Alaska Range orogen north of the Denali fault dip as steeply as 25°N and extend to depths as great as 20 km. These reflections outline a relict crustal architecture that in the past 20 yr has produced little seismicity. The Denali fault is nonreflective, probably because this fault dips steeply to vertical. The most intriguing finding from geophysical data is that earthquake aftershocks occurred above a rock body, with low electrical resistivity (>10 Ω·m), that is at depths below ∼10 km. Aftershocks of the Denali fault earthquake have mainly occurred shallower than 10 km. A high geothermal gradient may cause the shallow seismicity. Another possibility is that the low resistivity results from fluids, which could have played a role in locating the aftershock zone by reducing rock friction within the middle and lower crust.

Alaska↗

USGS2009

Earthquake stress drops and inferred fault strength on the Hayward Fault, east San Francisco Bay, California

We study variations in earthquake stress drop with respect to depth, faulting regime, creeping versus locked fault behavior, and wall-rock geology. We use the P-wave displacement spectra from borehole seismic recordings of M 1.0-4.2 earthquakes in the east San Francisco Bay to estimate stress drop using a stack-and-invert empirical Green's function method. The median stress drop is 8.7 MPa, and most stress drops are in the range between 0.4 and 130 MPa. An apparent correlation between stress drop and magnitude is entirely an artifact of the limited frequency band of 4-55 Hz. There is a trend of increasing stress drop with depth, with a median stress drop of ~5 MPa for 1-7 km depth, ~10 MPa for 7-13 km depth, and ~50 MPa deeper than 13 km. We use S=P amplitude ratios measured from the borehole records to better constrain the first-motion focal mechanisms. High stress drops are observed for a deep cluster of thrust-faulting earthquakes. The correlation of stress drops with depth and faulting regime implies that stress drop is related to the applied shear stress. We compare the spatial distribution of stress drops on the Hayward fault to a model of creeping versus locked behavior of the fault and find that high stress drops are concentrated around the major locked patch near Oakland. This also suggests a connection between stress drop and applied shear stress, as the locked patch may experience higher applied shear stress as a result of the difference in cumulative slip or the presence of higher-strength material. The stress drops do not directly correlate with the strength of the proposed wall-rock geology at depth, suggesting that the relationship between fault strength and the strength of the wall rock is complex.

Bulletin of the Seismological Society of America↗

USGS2015

Fluid-faulting interactions: Fracture-mesh and fault-valve behavior in the February 2014 Mammoth Mountain, California, earthquake swarm

Faulting and fluid transport in the subsurface are highly coupled processes, which may manifest seismically as earthquake swarms. A swarm in February 2014 beneath densely monitored Mammoth Mountain, California, provides an opportunity to witness these interactions in high resolution. Toward this goal, we employ massive waveform-correlation-based event detection and relative relocation, which quadruples the swarm catalog to more than 6000 earthquakes and produces high-precision locations even for very small events. The swarm's main seismic zone forms a distributed fracture mesh, with individual faults activated in short earthquake bursts. The largest event of the sequence, M 3.1, apparently acted as a fault valve and was followed by a distinct wave of earthquakes propagating ~1 km westward from the updip edge of rupture, 1–2 h later. Late in the swarm, multiple small, shallower subsidiary faults activated with pronounced hypocenter migration, suggesting that a broader fluid pressure pulse propagated through the subsurface.

California↗

USGS1991

Segmentation and the coseismic behavior of Basin and Range normal faults: examples from east-central Idaho and southwestern Montana, U.S.A.

The range-front normal faults of the Lost River and Lemhi Ranges, and the Beaverhead and Tendoy Mountains in east-central Idaho and southwestern Montana have well-preserved fault scarps on Quaternary deposits along much of their lengths. Fault-scarp morphology, the age of deposits displaced by the faults, and the morphology of the range fronts provide a basis for dividing the faults into segments that are typically 20–25 km long. The Lost River, Lemhi and Beaverhead fault zones are 141–151 km long, and each has six segments. The 60-km-long Red Rock fault (the range-front fault of the Tendoy Mountains) has two central segments that have been active in late Quaternary time; these two segments span the central 27 km of the fault. We recognize four characteristics that help to identify segment boundaries: (1) major en échelon offsets or pronounced gaps in the continuity of fault scarps; (2) distinct, persistent, along-strike changes in fault-scarp morphology that indicate different ages of faulting; (3) major salients in the range front; and (4) transverse bedrock ridges where the cumulative throw is low compared to other places along the fault zone. Only features whose size is measured on the scale of kilometers are regarded as significant enough to represent a segment boundary that could inhibit or halt a propagating rupture.

Journal of Structural Geology↗

USGS2024

Paleoseismology of the Sawtooth fault and implications for fault behavior in the epicentral region of the 2020 Mw 6.5 Stanley, Idaho, earthquake

The 2020 moment magnitude ( M w ⁠⁠ ) 6.5 Stanley, Idaho, earthquake raised questions about the history and extent of complex faulting in the northwestern Centennial Tectonic Belt (CTB) and its relation to the Sawtooth normal fault and Eocene Trans‐Challis fault system (TCFS). To explore faulting in this area, we excavated a paleoseismic trench across the Sawtooth fault along the western margin of the CTB, and compared an early Holocene (9.1 ± 2.1 ka, 1δ ⁠ ) rupture at the site with lacustrine paleoseismic data and fault mapping in the 2020 epicentral region. We find: (1) a history of partial to full rupture of the Sawtooth fault ( M w ⁠ 6.8–7.4), (2) that shorter ruptures ( M w ≤ ⁠⁠6.9 ) are likely along distributed and discontinuous faults in the epicentral region, (3) that this complex system that hosted the 2020 earthquake is not directly linked to the Sawtooth fault, (4) that the northeast‐trending TCFS likely plays a role in controlling fault length and rupture continuity for adjacent faults, and (5) that parts of the TCFS may facilitate displacement transfer between normal faults that accommodate crustal extension and rotation. Our results help unravel complex faulting in the CTB and imply that relict structures can help inform regional seismic hazard assessments.

Idaho↗

USGS2006

Continuous borehole strain and pore pressure in the near field of the 28 September 2004 M 6.0 Parkfield, California, earthquake: Implications for nucleation, fault response, earthquake prediction and tremor

Near-field observations of high-precision borehole strain and pore pressure, show no indication of coherent accelerating strain or pore pressure during the weeks to seconds before the 28 September 2004 M 6.0 Parkfield earthquake. Minor changes in strain rate did occur at a few sites during the last 24 hr before the earthquake but these changes are neither significant nor have the form expected for strain during slip coalescence initiating fault failure. Seconds before the event, strain is stable at the 10 −11 level. Final prerupture nucleation slip in the hypocentral region is constrained to have a moment less than 2 × 10 12 N m ( M 2.2) and a source size less than 30 m. Ground displacement data indicate similar constraints. Localized rupture nucleation and runaway precludes useful prediction of damaging earthquakes. Coseismic dynamic strains of about 10 microstrain peak-to-peak were superimposed on volumetric strain offsets of about 0.5 microstrain to the northwest of the epicenter and about 0.2 microstrain to the southeast of the epicenter, consistent with right lateral slip. Observed strain and Global Positioning System ( gps ) offsets can be simply fit with 20 cm of slip between 4 and 10 km on a 20-km segment of the fault north of Gold Hill ( M 0 = 7 × 10 17 N m). Variable slip inversion models using gps data and seismic data indicate similar moments. Observed postseismic strain is 60% to 300% of the coseismic strain, indicating incomplete release of accumulated strain. No measurable change in fault zone compliance preceding or following the earthquake is indicated by stable earth tidal response. No indications of strain change accompany nonvolcanic tremor events reported prior to and following the earthquake.

California↗

USGS2021

Improved scaling relationships for seismic moment and average slip of strike-slip earthquakes incorporating fault slip rate, fault width and stress drop

We develop a self‐consistent scaling model relating magnitude M w to surface rupture length ( ⁠L E ⁠ ), surface displacement D E ⁠ , and rupture width W E ⁠ , for strike‐slip faults. Knowledge of the long‐term fault‐slip rate S F improves magnitude estimates. Data are collected for 55 ground‐rupturing strike‐slip earthquakes that have geological estimates of L E ⁠ , D E ⁠ , and S F⁠ , and geophysical estimates of W E ⁠ . We begin with the model of Anderson et al. (2017) , which uses a closed form equation for the seismic moment of a surface‐rupturing strike‐slip fault of arbitrary aspect ratio and given stress drop, Δτ C ⁠ . Using W E estimates does not improve M w estimates. However, measurements of D E plus the relationship between Δτ C and surface slip provide an alternate approach to study W E ⁠ . A grid of plausible stress drop and width pairs were used to predict displacement and earthquake magnitude. A likelihood function was computed from within the uncertainty ranges of the corresponding observed M w and D E values. After maximizing likelihoods over earthquakes in length bins, we found the most likely values of W E for constant stress drop; these depend on the rupture length. The best‐fitting model has the surprising form W E ∝logL E —a gentle increase in width with rupture length. Residuals from this model are convincingly correlated to the fault‐slip rate and also show a weak correlation with the crustal thickness. The resulting model thus supports a constant stress drop for ruptures of all lengths, consistent with teleseismic observation. The approach can be extended to test other observable factors that might improve the predictability of magnitude from a mapped fault for seismic hazard analyses.

Bulletin of the Seismological Society of America↗

USGS2002

A preliminary study on fine structures of Jiashi earthquake region and earthquake generating fault

It is very unusual that nine large earthquakes of similar magnitudes (M = 6.1-6.8) occured within a very small area and a very short period of time (1997-1998) in Jiashi of Xinjiang Province, Northwest China. This paper analyzes the observed data of the aftershocks in the Jiashi earthquake region for studying the generating mechanism and deep structural background of the Jiashi strong earthquake swarm. The simultaneous inversion method was used to calculate the hypocenter positions and 3-D velocity structure of this region. The results show that the aftershocks concentrated in a NNE-trending belt, which roughly coincides with the NE-trending belt of the two strong earthquake belts. Velocity structure obtained from 3-D inversion suggests that there exist two low velocity zones, one trending NNE and the other NNW, below the depth of 12 km. These low velocity zones are almost consistent with the two strong earthquake belts. The preliminary results lead to the conclusion that the low velocity zones correspond to two deep crustal faults. At the time of our observation, microearthquakes took place on the NNE-trending fault, while the NNW-trending fault was relatively quiescent.

Acta Geophysica Sinica↗

USGS1975

Maps showing maximum earthquake intensity predicted in the southern San Francisco Bay region, California, for large earthquakes on the San Andreas and Hayward Faults

This map shows maximum earthquake intensity predicted at specific sites using the empirical relations derived from the reliable 1906 intensity data (figs. 3 and 4; see text). The numbers 4-0 correspond to letters A-E, respectively, of the San Francisco intensity scale. The predicted intensity value shown for each site is the maximum of those predicted for the site assuming that a large earthquake were to occur on either the San Andreas or the Hayward fault. The map suggests that an earthquake on either fault could cause as much damage at some sites distant from the faults as at sites in the immediate zone of potential surface faulting.

California↗

USGS2011

Earthquake rupture at focal depth, part II: mechanics of the 2004 M2.2 earthquake along the Pretorius Fault, TauTona Mine, South Africa

We analyze here the rupture mechanics of the 2004, M2.2 earthquake based on our observations and measurements at focal depth (Part I). This event ruptured the Archean Pretorius fault that has been inactive for at least 2 Ga, and was reactivated due to mining operations down to a depth of 3.6 km depth. Thus, it was expected that the Pretorius fault zone will fail similarly to an intact rock body independently of its ancient healed structure. Our analysis reveals a few puzzling features of the M2.2 rupture-zone: (1) the earthquake ruptured four, non-parallel, cataclasite bearing segments of the ancient Pretorius fault-zone; (2) slip occurred almost exclusively along the cataclasite-host rock contacts of the slipping segments; (3) the local in-situ stress field is not favorable to slip along any of these four segments; and (4) the Archean cataclasite is pervasively sintered and cemented to become brittle and strong. To resolve these observations, we conducted rock mechanics experiments on the fault-rocks and host-rocks and found a strong mechanical contrast between the quartzitic cataclasite zones, with elastic-brittle rheology, and the host quartzites, with damage, elastic–plastic rheology. The finite-element modeling of a heterogeneous fault-zone with the measured mechanical contrast indicates that the slip is likely to reactivate the ancient cataclasite-bearing segments, as observed, due to the strong mechanical contrast between the cataclasite and the host quartzitic rock.

Tautona Mine↗

USGS2022

Large surface-rupture gaps and low surface fault slip of the 2021 Mw 7.4 Maduo earthquake along a low-activity strike-slip fault, Tibetan Plateau

Based on field investigations, interpretations of high-resolution UAV images, and analyses of available InSAR data, we mapped the fault geometry and surface ruptures of the 2021 M w 7.4 Maduo earthquake that occurred on a low-activity strike-slip fault within the Tibetan Plateau. The results indicate that (a) the earthquake activated a fault that is ∼161 km long and has complicated structural geometry; (b) the surface rupture occurs over a distance of 148 km, but is separated into three distinct segments by two large gaps (38 and 20 km, respectively); (c) within the surface-rupture segments, the horizontal and vertical displacements are typically 0.2–2.6 m (much lower than the InSAR-based slip maximum of 2–6 m at depth) and ≤0.4 m, respectively. The two large gaps of the Maduo surface rupture represent the two largest surface-rupture discontinuities of strike-slip earthquakes ever documented, and coincide with structurally complicated fault portions and near-surface soft sediments.

Tibetan Plateau↗

USGS2023

3-D wave propagation simulations of Mw 6.5+ earthquakes on the Tacoma Fault, Washington state, considering the effects of topography, a geotechnical gradient, and a fault damage zone

We simulate shaking in Tacoma, Washington, and surrounding areas from M w 6.5 and 7.0 earthquakes on the Tacoma fault. Ground motions are directly modeled up to 2.5 Hz using kinematic, finite‐fault sources; a 3D seismic velocity model considering regional geology; and a model mesh with 30 m sampling at the ground surface. In addition, we explore how adjustments to the seismic velocity model affect predicted shaking over a range of periods. These adjustments include the addition of a region‐specific geotechnical gradient, surface topography, and a fault damage zone. We find that the simulated shaking tends to be near estimates from empirical ground‐motion models (GMMs). However, long‐period ( T = 5.0 s) shaking within the Tacoma basin is typically underpredicted by the GMMs. The fit between simulated and GMM‐derived short‐period ( T = 0.5 s) shaking is significantly improved with the addition of the geotechnical gradient. From comparing different M w 6.5 earthquake scenarios, we also find that the response of the Tacoma basin is sensitive to the azimuth of incoming seismic waves. In adding surface topography to the simulation, we find that average ground motion is similar to that produced from the nontopography model. However, shaking is often amplified at topographic highs and deamplified at topographic lows, and the wavefield undergoes extensive scattering. Adding a fault damage zone has the effect of amplifying short‐period shaking adjacent to the fault, while reducing far‐field shaking. Intermediate‐period shaking is amplified within the Tacoma basin, likely due to enhanced surface‐wave generation attributable to the fault damage zone waveguide. When applied in the same model, the topography and fault damage zone adjustments often enhance or reduce the effects of one another, adding further complexity to the wavefield. These results emphasize the importance of improving near‐surface velocity model resolution as waveform simulations progress toward higher frequencies.

Washington↗