This study presents the first paleoseismic investigation of the Middle America subduction zone at the Nicoya Peninsula, Costa Rica. This megathrust has been intensely studied over the past decade using a range of geologic and geophysical techniques, and it experienced interplate rupture in 2012 (moment magnitude 7.6). Despite many factors that could hinder preservation of a paleoseismic record in this coastal environment, including complex deposition in a tropical mangrove setting, this reconnaissance identifies two sites where stratigraphic evidence may record relative sea-level changes associated with Holocene earthquakes. Although more work is required to better constrain the timing and nature of these events, this study suggests that the Tamarindo and Playa Carrillo estuaries contain possible paleoseismic records. At the main study site of Tamarindo, alternations between mud and peat below 1 m in depth may record relative sea-level change associated with multiple earthquakes between similar to 5 and 8 ka. However, this site offers no paleoseismic evidence of late-Holocene earthquakes. Much younger stratigraphy occurs at a Playa Carrillo, where mud-peat alternations from 200 to 500 years ago could represent recent coseismic ground motions. The work presented here is limited to litho-and chronostratigraphy, however, and full interpretation of the relative sea-level histories of both sites will require quantitative, high-resolution biostratigraphic analysis. Although the results suggest paleoseismic records exist along the Nicoya Peninsula, they appear fragmentary and complex and ultimately may not provide a continuous, high-resolution paleoseismic record like those obtained at other subduction zones worldwide.

Coastal Sediments 2015 (2015) No AccessBEACHROCK HORIZONS OF THE NICOYA PENINSULA, COSTA RICA: GEOMORPHOLOGY, PETROLOGY, AND NEOTECTONIC SIGNIFICANCEJEFFREY MARSHALL, ANDREW BARNHART, AMBER BUTCHER, CLAYTON FREIMUTH, FOOKGIIN KHAW, ELI LAFROMBOISE, MICHAEL LANDEROS, SHAWN MORRISH, ELIZABETH OLSON, BRENT RITZINGER, DUSTIN STEWART, JOHN UTICK, KACIE WELLINGTON, LILIBETH WENCESLAO, THOMAS GARDNER, DAVID HARBOR, and STEPHEN OSBORNJEFFREY MARSHALLGeological Sciences Department, Cal Poly Pomona, Pomona, CA 91768, USA, ANDREW BARNHARTGeological Sciences Department, Cal Poly Pomona, Pomona, CA 91768, USA, AMBER BUTCHERGeological Sciences Department, Cal Poly Pomona, Pomona, CA 91768, USA, CLAYTON FREIMUTHGeosciences Department, Trinity University, San Antonio, TX 78212, USA, FOOKGIIN KHAWGeological Sciences Department, Cal Poly Pomona, Pomona, CA 91768, USA, ELI LAFROMBOISEGeological Sciences Department, Cal Poly Pomona, Pomona, CA 91768, USA, MICHAEL LANDEROSGeological Sciences Department, Cal Poly Pomona, Pomona, CA 91768, USA, SHAWN MORRISHGeological Sciences Department, Cal Poly Pomona, Pomona, CA 91768, USA, ELIZABETH OLSONDepartment of Geology, Washington & Lee University, Lexington, VA 24450, USA, BRENT RITZINGERGeological Sciences Department, Cal Poly Pomona, Pomona, CA 91768, USA, DUSTIN STEWARTGeological Sciences Department, Cal Poly Pomona, Pomona, CA 91768, USA, JOHN UTICKGeological Sciences Department, Cal Poly Pomona, Pomona, CA 91768, USA, KACIE WELLINGTONGeological Sciences Department, Cal Poly Pomona, Pomona, CA 91768, USA, LILIBETH WENCESLAOGeological Sciences Department, Cal Poly Pomona, Pomona, CA 91768, USA, THOMAS GARDNERGeosciences Department, Trinity University, San Antonio, TX 78212, USA, DAVID HARBORDepartment of Geology, Washington & Lee University, Lexington, VA 24450, USA, and STEPHEN OSBORNGeological Sciences Department, Cal Poly Pomona, Pomona, CA 91768, USAhttps://doi.org/10.1142/9789814689977_0252Cited by:2 PreviousNext AboutSectionsPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack CitationsRecommend to Library ShareShare onFacebookTwitterLinked InRedditEmail Abstract: We present results of geomorphic, petrologic, and hydrochemical analyses of carbonate beachrock deposits on the Nicoya Peninsula, Costa Rica. Beachrock horizons form near coastal streams and wetlands by precipitation of calcite and aragonite cement within beach face sediments along the zone of lowtide groundwater seepage. Carbonate precipitation occurs by mixing of phreatic and marine water, and evaporation of CO2-saturated spring water. Outcrops exhibit substantial lithologic and facies diversity, from well-sorted sandstones, to clastsupported conglomerates and matrix-rich breccias. Matrix sands consist of shell and coral fragments, mixed with lithic and mineral grains. Interstitial cements include acicular aragonite fringes, pore-filling sparry calcite, and circumgranular micritic rinds. Radiocarbon ages range from 0.5-4.0 ky for deposits on the modern beach, and 4.5-6.5 ky for uplifted terrace deposits. Progressive tectonic uplift resulting from repeated megathrust earthquakes elevates older horizons, exposing new beach sediments to cementation. Improved understanding of beachrock geomorphology facilitates its use in tracking vertical tectonic movements. FiguresReferencesRelatedDetailsCited By 2Sediment Characteristics of Beachrock: A Baseline Investigation Based on Microbial Induced Carbonate Precipitation at Krakal-Sadranan Beach, Yogyakarta, IndonesiaLutfian Rusdi Daryono, Kazunori Nakashima, Satoru Kawasaki, Anastasia Dewi Titisari and Didit Hadi Barianto10 January 2020 | Applied Sciences, Vol. 10, No. 2Management Tools for Safety in Costa Rica BeachesIsabel Arozarena Llopis and Alejandro Gutiérrez Echeverría5 December 2017 Coastal Sediments 2015Metrics History PDF download

Las zonas de subducción, los lugares donde convergen dos placas tectónicas, liberan alrededor del 90 porciento de la energía sísmica de nuestro planeta y generan los terremotos más grandes (Mw8.5). El comprender los procesos que se conjugan para crear estas amenazas de origen natural podría ayudar a reducir su impacto en la población y la infraestructura. El 5 de septiembre del 2012, a las 8:42 a.m ocurrió un terremoto de 7.6 grados de magnitud bajo la península de Nicoya, en el noroeste de Costa Rica. La gran mayoría de los terremotos de subducción en el mundo ocurren costa afuera; sin embargo este de Nicoya ocurrió en tierra firme bajo zonas pobladas. A pesar de ello, el terremoto de Nicoya del 2012 no provocó ninguna muerte y los daños que causó fueron muy pocos para un terremoto de esta magnitud y proximidad. Este terremoto no ocurrió de forma inesperada. Desde 1995 se venían haciendo evaluaciones del potencial sísmico de esta región clasificada como una brecha sísmica. Por más de una década antes del sismo se venía construyendo una red de monitoreo geodinámico en la península de Nicoya y sus alrededores, región bajo la cual se subduce la placa del Coco a casi 80 mm por año. Este proyecto internacional de cooperación multi-institucional tenía como objetivo aprovechar la oportunidad temporal de estar al final del ciclo sísmico. Además, se aprovechaba la ventaja geográfica de contar con una península directamente sobre la zona sismogénica de grandes sismos de subducción y poder así registrar, en el campo cercano, no solo el futuro terremoto sino también el proceso de acumulación de esfuerzos y la documentación de la historia de ruptura del terremoto. La información obtenida con dicha red permitió anticipar la ubicación y magnitud del inminente terremoto. Presentamos en este trabajo los antecedentes de esa anticipación y los detalles de lo ocurrido antes, durante y después de este terremoto, considerado quizás el terremoto de subducción mejor registrado de la historia Subduction zones, regions where two tectonic plates converge, are responsible of nearly 90 porcent of the energy released by our planet and cause the largest earthquakes (Mw8.5). Understanding the processes that conjúgate to produce these natural hazards could help reduce their impact on population and infrastructure. On September 5th, 2012, at 8:42 AM, a Mw=7.6 earthquake occurred under the Nicoya peninsula in Nw Costa Rica. Most subduction earthquakes occur offshore, but this Nicoya earthquake occurred on land under populated areas. Notwithstanding, the Nicoya 2012 earthquake did not cause human fatalities and damage in infrastructure was impressively low. This earthquake was not unexpected. Since 1995 several seismic potential assessments were published for this region, classified as a seismic gap. As part of an international cooperation project, a geodynamic network was built since the late 1990's on the Nicoya peninsula and its surroundings, where the Cocos plate subducts at nearly 80 mm/yr. With this project we were taking advantage of the temporal opportunity of being at the end of a seismic cycle. We were also benefitting from a geographical advantage of having a peninsula sitting right over the seismogenic zone of large earthquakes so we could record, in the near field, not only the incoming earthquake, but the process of stress build up and the history of rupture propagation. Information recorded by this network allowed us to anticipate the location and magnitude of the earthquake. In this work we are presenting a summary of the work done before, during and right after the Nicoya 2012 earthquake, which is perhaps the best recorded subduction earthquake

On 5 September 2012 a magnitude 7.6 earthquake occurred beneath the Nicoya Peninsula of northwestern Costa Rica, rupturing the subduction zone between the Cocos and Caribbean plates. In most subduction zones the locus of seismic slip lies far offshore, making it difficult to infer interface seismogenic processes from on‐shore observations. In contrast, the Nicoya Peninsula lies close to the trench (within 70 kilometers), allowing observations directly over the earthquake rupture zone.

Part of the subduction zone plate interface beneath Costa Rica was previously locked, which allowed strain to accumulate. Analyses using GPS and geomorphic data show that almost the entire locked region ruptured during a megathrust quake in 2012, implying that plate-interface mapping towards the end of the earthquake cycle can aid seismic hazard assessments.

The Atirro-Rio Sucio fault system forms a major northwest-trending strike-slip fault zone in east-central Costa Rica. We examined the kinematics and temporal evolution of this fault system through geomorphic, structural, and seismologic analysis. This 150-km-long strike-slip fault zone traverses the northern flank of the paleovolcanic Cordillera de Talamanca and extends northwestward into the active Cordillera Volcanica Central. Historical seismicity includes frequent minor swarms and occasional moderate-magnitude (M 5.0-6.5) damaging earthquakes. Field geomorphic evidence, fault kinematic data, and earthquake focal mechanisms are consistent in showing dextral slip along the mapped traces of northwest-striking faults. Continuity with other transcurrent faults in northwest Costa Rica indicates that the Atirro-Rio Sucio fault system may form the southeastern end of a regional network of northwest-trending dextral faults that accommodate margin-parallel displacement of the Central American forearc sliver. The Atirro-Rio Sucio fault system originates within the Central Costa Rica Deformed Belt inboard of the indenting Cocos Ridge. We infer that ridge collision drives lateral escape of crustal fragments northwestward along an array of dextral Central Costa Rica Deformed Belt faults including the major structures of the Atirro-Rio Sucio fault system. This zone of arc-parallel extrusion thus represents the root of the Central American forearc sliver. Consistent with recent geodynamic models, we propose that northwestward sliver escape along the Atirro-Rio Sucio faults is driven by rigid indentation of the aseismic Cocos Ridge into southern Costa Rica.

International field experiences offer exceptional opportunities for effective student learning in the geosciences. Over the 10 yr period between 1998 and 2008, more than 40 undergraduate students from 14 institutions participated in field research investigating active tectonics on the Nicoya Peninsula, Costa Rica. Three different project models were used: (1) a month-long summer research project, (2) a series of 1 to 2 wk independent field study projects, and (3) a week-long field research module. These projects shared a common research theme (active tectonics), field area (Nicoya Peninsula), and pedagogy (experiential learning), thus allowing for easy comparison of teaching methods, logistics, and learning outcomes. Each model has unique pedagogical benefits and challenges, and is therefore better suited for a different group size, student to faculty ratio, project duration, and budget. Collectively, these student research projects generated significant publishable data relevant to ongoing investigations of forearc tectonics and earthquake hazards along the Costa Rican Pacific margin. Individual student projects were carefully designed to provide a quality field learning experience, while adding a new piece to the larger research puzzle. Indicators of project success include levels of student engagement; gains in technical and cognitive field skills; and productivity of student-authored publications, reports, and presentations. Students commonly described these projects as instrumental in shaping their professional identity as geoscientists. Blending international field research with experiential learning pedagogy creates a powerful synergy that captures student imagination and motivates learning. By placing students beyond the comfort of their home learning environment, international field projects pique student curiosity, sharpen awareness and comprehension, and amplify the desire to learn. Experiential learning pedagogy encourages students to define their own research agenda and solve problems through critical thinking, inquiry, and reflection. The potent combination of international fieldwork and experiential learning helps students to develop the self-confidence and reasoning skills needed to solve multifaceted real-world problems, and provides exceptional training for graduate school and professional careers in the geosciences.

The Waratah Fault is a northeast trending, high angle, reverse fault in the Late Paleozoic Lachlan Fold Belt at Cape Liptrap on the Southeastern Australian Coast. It is susceptible to reactivation in the modern intraplate stress field in Southeast Australia and exhibits Late Pliocene to Late Pleistocene reactivation. Radiocarbon, optically stimulated luminescence (OSL), and cosmogenic radionuclide (CRN) dating of marine terraces on Cape Liptrap are used to constrain rates of displacement across the reactivated Waratah Fault. Six marine terraces, numbered Qt(6)-Tt(1) (youngest to oldest), are well developed at Cape Liptrap with altitudes ranging from similar to 1.5 m to similar to 170 m amsl, respectively. On the lowest terrace, Qt(6). barnacles in wave-cut notches similar to 1.5 m amsl, yielded a radiocarbon age of 6090-5880 Cal BP, and reflect the local mid-Holocene sea level highstand. Qt(5) yielded four OSL ages from scattered locations around the cape ranging from similar to 80 ka to similar to 130 ka. It formed during the Last Interglacial sea level highstand (MIS 5e) at similar to 125 ka. Inner edge elevations (approximate paleo high tide line) for Qt(5) occur at distinctly different elevations on opposite sides of the Waratah Fault. Offsets of the inner edges across the fault range from 1.3 m to 5.1 m with displacement rates ranging from 0.01 mm/a to 0.04 mm/a. The most extensive terrace, Tt(4), yielded four Early Pleistocene cosmogenic radionuclide (CRN) ages: two apparent burial ages of 0.858 Ma +/- 0.16 Ma and 1.25 +/- Ma 0.265 Ma, and two apparent exposure ages of 1.071 Ma +/- 0.071 Ma (Be-10) and 0.798 +/- Ma 0.066 Ma (Al-26). Allowing for muonic production effects from insufficient burial depths, the depth corrected CRN burial ages are 1.8 Ma +/- 0.56 Ma and 2.52 Ma +/- 0.88 Ma, or Late Pliocene. A Late Pliocene age is our preferred age. Offsets of Tt(4) across the Waratah Fault range from a minimum of similar to 20 m for terrace surface treads to a maximum of similar to 70 m for terrace bedrock straths. Calculated displacement rates for Tt(4) range from 0.01 mm/a to 0.04 mm/a (using a Late Pliocene age, similar to 2 Ma), identical to the rates calculated for the Last Interglacial terrace, Qt(5). This indicates that deformation at Cape Liptrap has been ongoing at similar time-averaged rates at least since the Late Pliocene. The upper terraces in the sequence, Tt(3) (similar to 110 m amsl), Tt(2) (similar to 140 m) and Tt(1) (similar to 180 m) are undated, but most likely correlate to sea level highstands in the Neogene. Terraces Tt1-Tt4 show an increasing northward tilt with age.The Waratah Fault forms a prominent structural boundary in the Lachlan Fold Belt discernible from airborne magnetic and bouger gravity anomalies. Seismicity and deformation are episodic. Episodic movement on the Waratah Fault may be coincident with sea level highstands since the Late Pliocene, possibly from increased loading and elevated pore pressure within the fault zone. This suggests that intervals between major seismic events Could be on the order of 100 ka. (C) 2008 Elsevier Ltd. All rights reserved.

Orthogonal subduction of bathymetrically rough oceanic lithosphere along the northwestern flank of the Cocos Ridge imprints a distinctive style of deformation on the overriding Costa Rican forearc. We divide the Costa Rican forearc into three 100-160-km-long deformational domains based on the bathymetric roughness and thickness of the Cocos plate entering the Middle American Trench, the dip of the subducting plate, the variation in surface uplift rates of late Quaternary coastal deposits, and the orientations and types of faults deforming Paleogene and Neogene sedimentary rocks. In the similar to 100-km-long Nicoya domain, coastal deposits show localized surface uplift and arcward tilting above the downdip projections of the fossil trace of the Cocos-Nazca-Panama (CO-NZ-PA) triple junction and the Fisher seamount and ridge. In the similar to 120-km-long central Pacific forearc domain between the Nicoya Peninsula and Quepos, shallower (similar to 60 degrees) subduction of seamounts and plateaus is accompanied by trench-perpendicular late Quaternary normal faults. Steeply dipping, northeast-striking, margin-perpendicular faults accommodate differential uplift associated with seamount subduction. Uplift and faulting differ between the segments of the forearc facing subducting seamounts and ridges. Inner forearc uplift along the seamount-dominated segment is greatest inboard of the largest furrows across the lower slope. Localized uplift and arcward tilting of coastal deposits is present adjacent to subducting seamounts. In contrast, inboard of the underthrusting aseismic Cocos Ridge, along the similar to 160-km-long Fila Costena domain between Quepos and the Burica Peninsula, mesoscale fault populations record active shortening related to the similar to 100-km-long Fila Costena fold-and-thrust belt. The observed patterns of faulting and permanent uplift are best explained by crustal thickening. The uplifted terraces provide a first-order estimate of permanent strain along the forearc in Costa Rica. The permanent strain recorded by uplift of these Quaternary surfaces exceeds the predicted rebound of stored elastic strain released during subduction-zone earthquakes.

Subduction of hotspot-thickened seafloor profoundly affects convergent margin tectonics, strongly affecting upper plate structure, volcanism, and landscape evolution. In southern Central America, low-angle subduction of the Cocos Ridge and seamount domain largely controls landscape evolution in the volcanic arc. Field mapping, stratigraphic correlation, and Ar-40/Ar-39 geochronology for late Cenozoic volcanic rocks of central Costa Rica provide new insights into the geomorphic response of volcanic arc landscapes to changes in subduction parameters (slab thickness, roughness, dip). Late Neogene volcanism was focused primarily along the now-extinct Cordillera de Aguacate. Quaternary migration of the magmatic front shifted volcanism northeastward to the Caribbean slope, creating a new topographic divide and forming the Valle Central basin. Stream capture across the paleo-Aguacate divide led to drainage reversal toward the Pacific slope and deep incision of reorganized fluvial networks. Pleistocene caldera activity generated silicic ash flows that buried the Valle Central and descended the Tarcoles gorge to the Orotina debris fan at the coast. Growth of the modern Cordillera Central accentuated relief along the new divide, establishing the Valle Central as a Pacific slope drainage basin. Arc migration, relocation of the Pacific-Caribbean drainage divide, and formation of the Valle Central basin resulted from slab shallowing as irregular, hotspot-thickened crust entered the subduction zone. The geomorphic evolution of volcanic arc landscapes is thus highly sensitive to changes in subducting plate character.

The southeastern tip of the Peninsula de Nicoya, Costa Rica, on the Caribbean plate margin lies inboard of the rough bathymetric terrain on the subducting Cocos plate and along the landward projection of the convergence vector for the Fisher seamount group. The southern tip of the peninsula has nearly orthogonal coastlines and extensive, well-preserved. Holocene marine terraces, and is ideally situated to evaluate the spatial distribution of forearc deformation in response to seamount subduction.Two marine terraces that yielded 35 radiocarbon dates give information on the rates, style, and timing of deformation along 40 km of coastline. Ages range from 3.5 to 7.4 ka for a higher terrace and from 0.3 to 2.9 ka for a lower terrace. A maximum uplift rate is similar to6.0 m/k.y. along the southeastern tip of the peninsula. Uplift rates decrease linearly to <1.0 m/k.y. along both orthogonal coastlines and thus landward from the Middle America Trench and away from the line of subducting seamounts. The 400 km(2) region along the tip of the peninsula can be approximated as a rotating block with an angular rotation rate of 0.02 degrees /k.y. about an axis with an azimuth of 80 degrees. Given the modern elevation and dip of the late Quaternary Cobano surface, this style of deformation is limited to a duration of 100-200 k.y. Deformation is occurring in response to seamount bypass or underplating onto the Caribbean plate margin.

Fault kinematics, seismicity, and geodetic data across central Costa Rica reveal a diffuse fault zone, here named the Central Costa Rica Deformed Belt (CCRDB). The CCRDB defines the western margin of the Panama block and links the North Panama Deformed Belt (NPDB) along the Caribbean coast with the Middle America Trench (MAT) along the Pacific coast. The junction of the CCRDB and the MAT coincides with an abrupt transition from smooth to rough crust on the subducting Cocos plate (rough‐smooth boundary). Shallow subduction of rough, thickened oceanic crust associated with the Cocos Ridge shifts active shortening into the volcanic arc along faults of the CCRDB. Variable fault kinematics along this zone may reflect three combined deformation mechanisms: horizontal shortening and shear from oceanic ridge indentation, basal traction from shallow subduction, and localized block uplift from subducting seamount roughness. Within the forearc (domain 1), mesoscale faults express transtension where steep NE striking regional‐scale faults intersect the Pacific coast. Across the volcanic arc (domain 2), mesoscale faults exhibit mostly sinistral and dextral slip on NE and NW striking conjugate faults, respectively. Approaching the NPDB in the back arc (domain 3), transcurrent faulting is modified by transpression and crustal thickening. Fault kinematics are consistent with earthquake focal mechanisms and Global Positioning System (GPS) measurements. Radiometric age constraints confirm that faulting postdates the late Neogene onset of shallow subduction. The ensuing deformation front has propagated northward into the volcanic arc to its present position along the seismically active CCRDB. Within the forearc, the effect of shallow subduction is overprinted by local uplift related to underthrusting seamounts.

Fault kinematics and uplift in the Costa Rican fore me of the Middle America convergent margin are controlled to a large extent by roughness on the subducting Cocos plate. Along the northwest flank of the incoming Cocos Ridge, seafloor is characterized by short wavelength roughness related to northeast-trending seamount chains. Onland projection of the rough subducting crust coincides with a system of active faults oriented at high angles to the margin that segment the fore-are thrust belt and separate blocks with contrasting uplift rates. Trunk segments of Pacific slope fluvial systems typically follow these margin-perpendicular faults. Regionally developed marine and fluvial terraces are correlated between drainages and across faults along the Costa Rican Pacific coast. Terrace separations across block-bounding faults reveal a pattern of fore-are uplift that coincides roughly with the distribution of incoming seamounts. Magnitude and distribution of Quaternary uplift along the Costa Rican Pacific coast suggests that, despite a thin incoming sediment pile, the inner fore are shows an accumulation of mass-a characteristic that may be due to underplating of seamounts beneath the fore-are high.