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Trench‐parallel translation of the Central American Forearc (CAFA) is the result of strain partitioning along the Cocos and Caribbean (CA) convergent margin. Unlike the tectonics of northwestern Costa Rica and El Salvador, CAFA‐CA relative motion in Nicaragua is not accommodated on margin‐parallel fault systems. Rather, the northwest‐trending dextral shear is accommodated on margin‐normal sinistral strike‐slip faults that approximate the motion of a margin‐parallel fault (i.e., bookshelf faulting). We compare a new Global Positioning System interseismic horizontal velocity field to analytical and numerical models to show that the bookshelf faulting model can produce the observed velocity field and provide insight into the kinematics and configuration of the margin‐normal fault system. We find that a fault system with 20 km‐long parallel to sub‐parallel margin‐normal sinistral faults, spaced ∼5 km apart, locked from the surface to 5 km depth, and with interseismic slip deficits of 4 mm yr−1, can replicate the observed velocity field. These findings have implications for the region's seismic hazard where shallow moderate‐magnitude earthquakes will have reoccurrence intervals of ∼50 years. These findings are also important for volcanic hazard estimation and unrest forecasting because the margin‐normal faults are in the volcanic arc and magma‐tectonic interactions have been documented along the CAFA. The Central American Forearc (CAFA) is a northwest‐moving tectonic block that is located between the Middle America Trench and the Central American Volcanic Arc (CAVA). Northwest‐oriented faults (i.e., faults parallel to the CAVA motion), have been found in Costa Rica, El Salvador, and Guatemala, representing the boundary between CAFA and CAVA. In eastern El Salvador, Nicaragua, and western Costa Rica, a different fault style has been identified where the faults are oriented perpendicular to the motion of the CAVA (bookshelf faulting). These faults are ancient structures that take up the motion between the CAFA and CAVA, which is easier than creating new faults parallel to the motion. We show that, in northwestern Nicaragua, the bookshelf faulting can produce the observed GPS data. We find that these faults should move at 4 mm/yr, are close to populated areas, and will produce M5 to M6 earthquakes every 50 years. Bookshelf faulting accommodates northwest‐directed forearc motion on margin‐normal sinistral faultsStrain accumulation on margin‐normal sinistral faults agrees with GPS‐derived horizontal velocity field in northwestern NicaraguaShallow M> 5 upper‐plate earthquakes in the region will have reoccurrence intervals of ∼50 years Bookshelf faulting accommodates northwest‐directed forearc motion on margin‐normal sinistral faults Strain accumulation on margin‐normal sinistral faults agrees with GPS‐derived horizontal velocity field in northwestern Nicaragua Shallow M> 5 upper‐plate earthquakes in the region will have reoccurrence intervals of ∼50 years

We reevaluate the 72?year history of surface slip on the North Anatolian Fault at Ismetpasa since the Mw?=?7.4 1944 Bolu/Gerede earthquake. A revised analysis of published observations suggests that days after the earthquake the fault had been offset by 3.7?m and 6?years later by an additional 0.74?m. Creep was first recognized on the fault in 1969 as a 0.13?m offset of a wall constructed in 1957 that now (2016) has been offset by 0.52?m. A carbon rod creep meter operated across the fault in the past 2?years confirms results from an invar wire creep meter operated 1982–1991 that surface slip is episodic. Months of fault inactivity are interrupted by slow slip (=10?µm/d) or multiple creep events with cumulative amplitudes of 2–10?mm, durations of several weeks, and with slip rates briefly exceeding >2.5?mm/h. Creep events accommodate 80% of the surface slip and individually release?˜?10-6shear strain on the flanks of the uppermost 3–7?km of the fault. GPS and interferometric synthetic aperture radar methods yield a current fault slip rate of 7.6?±?1?mm/yr suggesting that creep meters incompletely sample the full width of the surface shear zone. The slip rate has slowed from >10?mm/yr in 1969 to 6.1?mm/yr at present, 4.65?mm/yr of which appears to be due to steady interseismic creep driven by plate boundary stressing rates. We calculate that a further 1?m of aseismic surface slip will precede the next major earthquake on the fault assuming an?˜?260?year main shock recurrence interval on this segment. We describe slow surface slip on the North Anatolian fault in Turkey, similar to that occurring on the San Andreas and Hayward Faults of California. Rapid slip was initiated by a magnitude 7.4 earthquake in 1944 (several inches/year) but by 1969 it had slowed to less than 1/2? per year and by 2016 had slowed to 1/4? per year. The slip occurs in brief episodes at roughly 8 month intervals with durations of a few hours to weeks, and appears to be confined to the uppermost 3 miles of the 7 mile deep fault. When it occurs this slip stresses the top of the region at depth that slips in large earthquakes, suggesting that monitoring surface slip close to the anticipated time of the next earthquake may provide an indication of the imminence of its occurrence. Afterslip decayed rapidly in the first two decades following the 1944 Mw=7.4 Bolu earthquake, and surface slip is now driven almost entirely by plate boundary shear stressEighty percent of surface creep (~ 7 mm/yr) on the North Anatolian Fault near Ismetpasa occurs as creep events in the top 5 kmCreep events with 2-10 mm amplitudes increment stress in the upper 5 km of the Anatolian Fault at ~ 8 month intervals

Strain partitioning in oblique convergent margins results in margin‐parallel shear in the overriding plate. Margin‐parallel shear is often accommodated by margin‐parallel strike‐slip faults proximal to active volcanic arcs. Along the Nicaraguan segment of the Central American Forearc (CAFA) in the Cocos‐Caribbean plate convergent margin, there are no well‐expressed right‐lateral faults that accommodate CA‐CAFA relative motion. Instead, historical earthquakes and mapped fault orientations indicate that the ∼12 mm/yr of dextral motion is accommodated on arc‐normal, left‐lateral faults (i.e., bookshelf faults). We investigate three upper‐plate earthquakes; the 10 April 2014 (Mw6.1), 15 September 2016 (Mw5.7), and 28 September 2016 (Mw5.5), using Global Position System co‐seismic displacements and relocated earthquake aftershocks. Our analyses of the three earthquakes indicate that the 10 April 2014 earthquake ruptured an unmapped margin‐parallel right‐lateral fault in Lago Xolotlán (Managua) and the September 2016 earthquakes ruptured arc‐normal, left‐lateral and oblique‐slip faults. These earthquakes represent a triggered sequence whereby the 10 April 2014 earthquake promoted failure of the faults that ruptured in September 2016 by imparting a static Coulomb stress change (ΔCFS) of 0.02–0.07 MPa. Likewise, the 15 September 2016, earthquake additionally promoted failure (ΔCFS of 0.08–0.1 MPa) on sub‐parallel faults that ruptured in two subsequent earthquakes. We also present an instance of magma‐tectonic interaction whereby the 10 April 2014 earthquake dilated (10s of μStrain) the shallow magmatic system of Momotombo Volcano, which led to magma injection, ascent, and eruption on 1 December 2015, after ∼100 years of quiescence. The tectonic boundary between the northwest migrating Central American Forearc (CAFA), located between the active Central American Volcanic Arc and the Middle America Trench, and the CA plate poses significant seismic and volcanic hazards. Shallow, damaging earthquakes occur along the boundary and within close proximity to volcanic centers. We present models of GPS‐derived co‐seismic displacements and relocated seismicity that indicate these earthquakes primarily occur on faults perpendicular to the forearc, unlike most global analogs where motion is accommodated by faults parallel to the margin. Our analysis of these earthquakes also shows that they are a triggered sequence, where each earthquake primed nearby faults for failure, resulting in subsequent earthquakes. The triggered earthquake sequence has implications for seismicity migrating through the forearc and short‐ (years) to medium‐term (decadal) seismic forecasting. We also found that one of the earthquakes perturbed the Momotombo Volcano magmatic system thereby allowing the movement of magma, which lead to an eruption. Three upper‐plate earthquakes show Central American Forearc‐CA plate motion is primarily accommodated by left‐lateral arc‐normal faultsThe three upper‐plate earthquakes were a triggered sequence, indicating stress migration through the arcThe 10 April 2014 earthquake dilated the Momotombo magma system, allowing magma injection and ascent, leading to the 2015 eruption Three upper‐plate earthquakes show Central American Forearc‐CA plate motion is primarily accommodated by left‐lateral arc‐normal faults The three upper‐plate earthquakes were a triggered sequence, indicating stress migration through the arc The 10 April 2014 earthquake dilated the Momotombo magma system, allowing magma injection and ascent, leading to the 2015 eruption