Geology topics

Chris Madden

Publications and source records attributed to Chris Madden.

3 recordsLinked to original sources

USGS2013

Integrated carbon budget models for the Everglades terrestrial-coastal-oceanic gradient: Current status and needs for inter-site comparisons

Recent studies suggest that coastal ecosystems can bury significantly more C than tropical forests, indicating that continued coastal development and exposure to sea level rise and storms will have global biogeochemical consequences. The Florida Coastal Everglades Long Term Ecological Research (FCE LTER) site provides an excellent subtropical system for examining carbon (C) balance because of its exposure to historical changes in freshwater distribution and sea level rise and its history of significant long-term carbon-cycling studies. FCE LTER scientists used net ecosystem C balance and net ecosystem exchange data to estimate C budgets for riverine mangrove, freshwater marsh, and seagrass meadows, providing insights into the magnitude of C accumulation and lateral aquatic C transport. Rates of net C production in the riverine mangrove forest exceeded those reported for many tropical systems, including terrestrial forests, but there are considerable uncertainties around those estimates due to the high potential for gain and loss of C through aquatic fluxes. C production was approximately balanced between gain and loss in Everglades marshes; however, the contribution of periphyton increases uncertainty in these estimates. Moreover, while the approaches used for these initial estimates were informative, a resolved approach for addressing areas of uncertainty is critically needed for coastal wetland ecosystems. Once resolved, these C balance estimates, in conjunction with an understanding of drivers and key ecosystem feedbacks, can inform cross-system studies of ecosystem response to long-term changes in climate, hydrologic management, and other land use along coastlines

Florida↗

USGS2010

Neotectonics and paleoseismology of the Limón and pedro miguel faults in Panamá: earthquake hazard to the Panamá canal

We present new geologic, tectonic geomorphic, and geochronologic data on the slip rate, timing, and size of past surface ruptures for the right-lateral Lim??n and Pedro Miguel faults in central Panam??. These faults are part of a system of conjugate faults that accommodate the internal deformation of Panam?? resulting from the ongoing collision of Central and South America. There have been at least three surface ruptures on the Lim??n fault in the past 950-1400 years, with the most recent during the past 365 years. Displacement in this young event is at least 1.2 m (based on trenching) and may be 1.6-2 m (based on small channel offsets). Awell-preserved 4.2 m offset suggests that the penultimate event also sustained significant displacement. The Holocene slip rate has averaged about 6 mm=yr, based on a 30-m offset terrace riser incised into a 5-ka abandoned channel. The Pedro Miguel fault has sustained three surface ruptures in the past 1600 years, the most recent being the 2 May 1621 earthquake that partially destroyed Panam?? Viejo. At least 2.1 m of slip occurred in this event near the Canal, with geomorphic offsets suggesting 2.5-3 m. The historic Camino de Cruces is offset 2.8 m, indicating multimeter displacement over at least 20 km of fault length. Channel offsets of 100-400 m, together with a climate-induced incision model, suggest a Late Quaternary slip rate of about 5 mm=yr, which is consistent with the paleoseismic results. Comparison of the timing of surface ruptures between the Lim??n and Pedro Miguel faults suggests that large earthquakes may rupture both faults with 2-3 m of displacement for over 40 km, such as is likely in earthquakes in the M 7 range. Altogether, our observations indicate that the Lim??n and Pedro Miguel faults represent a significant seismic hazard to central Panam?? and, specifically, to the Canal and Panam?? City.

Bulletin of the Seismological Society of America↗

USGS2009

Palaeoseismology of the Vilariça segment of the Manteigas-Bragança fault in northeastern Portugal

The Manteigas-Bragança fault is a major, 250-km-long, NNE-striking, sinistral strike-slip structure in northern Portugal. This fault has no historical seismicity for large earthquakes, although it may have generated moderate (M5+) earthquakes in 1751 and 1858. Evidence of continued left horizontal displacement is shown by the presence of Cenozoic pull-apart basins as well as late Quaternary stream deflections. To investigate its recent slip history, a number of trenches were excavated at three sites along the Vilariça segment, north and south of the Douro River. At one site at Vale Meão winery, the occurrence of at least two and probably three events in the past 14.5 ka was determined, suggesting an average return period of about 5–7 ka. All three events appear to have occurred as a cluster in the interval between 14.5 and 11 ka, or shortly thereafter, suggesting a return period of less than 2 ka between events within the cluster. In the same area, a small offset rill suggests 2–2.5 m of slip in the most recent event and about 6.1 m after incision below a c . 16 ka alluvial fill event along the Douro River. At another site along the Vilariça River alluvial plain, NE of the Vale Meão site, several trenches were excavated in late Pleistocene and Holocene alluvium, and exposed the fault displacing channel deposits dated to between 18 and 23 ka. In a succession of closely spaced parallel cuts and trenches, the channel riser was traced into and across the fault to resolve c . 6.5 m of displacement after 18 ka and c . 9 m of slip after c . 23 ka. These observations yield a slip rate of 0.3–0.5 mm/a, which is consistent with earlier estimates. Combining the information on timing at Vale Meão winery and displacement at Vilariça argues for earthquakes in the M7+ range, with coseismic displacements of 2–3 m. This demonstrates that there are potential seismic sources in Portugal that are not associated with the 1755 Lisbon earthquake or the Tagus Valley, and, although rare, large events on the Vilariça fault could be quite destructive for the region. This work provides an analogue for the study of active faulting in intracontinental settings and supports the view that earthquakes within intracontinental settings tend to cluster in time. In addition, this study highlights the usefulness and application of multiple field, remote sensing and geochronological techniques for seismic hazard mitigation.

Manteigas - Braganca fault↗