Continental Transform Basins: Why Are They Asymmetric?

Abstract

Continental transforms constitute only a few of the world's plate boundaries and do not produce the largest earthquakes. Yet they are the tectonic underpinning of some of the most attractive and densely populated coastal environments. As a result, they have disproportionally contributed to catastrophic earthquakes. The most recent example is the M = 7.0 earthquake that struck Haiti on 12 January 2010, killing at least 100,000 people, by some reports. Because of concern for their earthquakes, continental transforms–particularly California's San Andreas Fault and Turkey's North Anatolian fault–have been intensely studied. Nonetheless, the link between the largest and most dangerous earthquakes and fault segments along transforms remains elusive. A better understanding of the structural singularities bounding these segments, particularly the subsurface nature of basins along transform faults, may clarify why some of them stop earthquake ruptures while others do not.

An earthquake gap south of Istanbul

“…The fault traces imaged by the seismicity correlate well with those identified from multi-channel seismic profiles showing that the sedimentary fill of the Cinarcik Basin extends as deep as 3-4 km (refs 14,15). Furthermore, the southward-dipping fault plane for the Princes Islands segment is in good accordance with a recently published model for the formation of the Cinarcik transform basin, in which subsidence is driven by oblique dip-slip on the Princes Islands fault segment 16 .…”

Neotectonics of the Owen Fracture Zone (NW Indian Ocean): Structural evolution of an oceanic strike-slip plate boundary

“…All pull‐apart basins developed along the OFZ are asymmetric (18°40′N, 20°N, Qalhat Basin). Asymmetric basins are commonly observed along strike‐slip faults [ Ben‐Avraham and Zoback , 1992; Brothers et al , 2009; Seeber et al , 2010] and interpreted as the result of transform normal extension. Asymmetry exists even at the scale of the sub‐basin SB3 of the 20°N Basin (Figure 6), which compares closely with the Zofar Basin along the Levant fault because of the reversal of its asymmetry [ Frieslander , 2000].…”

Stratigraphic record of basin development within the San Andreas fault system: Late Cenozoic Fish Creek-Vallecito basin, southern California

“…Sedimentary basins that form adjacent to transform faults offer unique insights into regional isostasy, strain partitioning, fault displacements, and kinematic evolution of strike-slip fault zones (e.g., Mann et al, 1983;Christie-Blick and Biddle, 1985;May et al, 1993;Crowell, 2003;Mann, 2007;Seeber et al, 2010). Stratigraphic studies allow us to track the initiation and development of continental transforms because motion on strike-slip faults typically produces local-to regional-scale crustal subsidence that leads to accumulation and preservation of sedimentary deposits.…”