The erosion of mountain belts controls their topographic and structural evolution and is the main source of sediment delivered to the oceans. Mountain erosion rates have been estimated from current relief and precipitation, but a more complete evaluation of the controls on erosion rates requires detailed measurements across a range of timescales. Here we report erosion rates in the Taiwan mountains estimated from modern river sediment loads, Holocene river incision and thermochronometry on a million-year scale. Estimated erosion rates within the actively deforming mountains are high (3-6 mm yr(-1)) on all timescales, but the pattern of erosion has changed over time in response to the migration of localized tectonic deformation. Modern, decadal-scale erosion rates correlate with historical seismicity and storm-driven runoff variability. The highest erosion rates are found where rapid deformation, high storm frequency and weak substrates coincide, despite low topographic relief.

No abstract

No abstract

Rapid shortening in convergent mountain belts is often accommodated by slip on faults at multiple levels in upper crust, but no geodetic observation of slip at multiple levels within hours of a moderate earthquake has been shown before. Here we show clear evidence of fault slip within a shallower thrust at 5–10 km depth in SW Taiwan triggered by the 2016 Mw 6.4 MeiNong earthquake at 15–20 km depth. We constrain the primary coseismic fault slip with kinematic modeling of seismic and geodetic measurements and constrain the triggered slip and fault geometry using synthetic aperture radar interferometry. The shallower thrust coincides with a proposed duplex located in a region of high fluid pressure and high interseismic uplift rate, and may be sensitive to stress perturbations. Our results imply that under tectonic conditions such as high‐background stress level and high fluid pressure, a moderate lower crustal earthquake can trigger faults at shallower depth.

No abstract

[1] On the basis of field observations and geodetic measurements we analyzed coseismic and postseismic deformation of the 2003, M w = 6.5, Chengkung earthquake across the rupture trace of the Chihshang fault, which lies along the suture zone between the Philippine Sea plate and the Eurasian plate in eastern Taiwan. At three of our investigation sites along the Chihshang fault the earthquake deformation was exhibited by fresh fractures within the 150-to 200-m-wide surface fault zone, reactivating preexisting fractures in most cases. In addition to daily recorded creep meter data, geodetic measurements, including leveling, distance-and-angle electronic distance meters, and GPS measurements, were carried out during surveys 20-25 days before, 20-25 days after, and 120-125 days after the earthquake. The near-fault surface deformation is mainly characterized by anticlinal folding in the hanging wall and minor gentle synclinal folding in the footwall. The geodetic data show that within our 150-to 250-m-wide networks the coseismic deformation of the main shock produced only about 1-2 cm of horizontal shortening and vertical offset across the fault zone. A larger additional displacement of about 7-9 cm for both the horizontal shortening and the vertical offset occurred as postseismic creep during the 120-125 days following the main shock. We interpret the predominant folding and the rather large postseismic creep as a result of strong velocity strengthening along the fault plane near the surface, which caused locking or coupling effect during the coseismic rupturing. The depth of locked segment, along which the coseismic and postseismic slip decreased dramatically upward, is estimated to be 25-100 m, depending on the site. We interpreted the velocity strengthening and coupling effect at the shallow level as viscoelastic behavior of unconsolidated deposits in the footwall and mélange mudstone in the hanging wall. By incorporating far-fault continuous GPS data, it was found that minor but significant deformation occurred outside of the surface ruptures zone of the Chihshang fault. In addition, a possible back thrust or back fold might have occurred in the hanging wall. We note that the Chengkung earthquake occurred during the dry season. This is consistent with the fact that the mechanical coupling of the fault at shallow depth is higher during drier periods, inferred from the previous seasonal creep data. At outcrop scale, regarding damage of construction such as a concrete retaining wall, most of the coseismic and postseismic horizontal shortening was essentially absorbed by multiple distributed brittle ruptures, which deserves attention in terms of earthquake hazard mitigation.

No abstract

No abstract