Neil Frazer

Doubling of coastal flooding frequency within decades due to sea-level rise

Global climate change drives sea-level rise, increasing the frequency of coastal flooding. In most coastal regions, the amount of sea-level rise occurring over years to decades is significantly smaller than normal ocean-level fluctuations caused by tides, waves, and storm surge. However, even gradual sea-level rise can rapidly increase the frequency and severity of coastal flooding. So far, global-scale estimates of increased coastal flooding due to sea-level rise have not considered elevated water levels due to waves, and thus underestimate the potential impact. Here we use extreme value theory to combine sea-level projections with wave, tide, and storm surge models to estimate increases in coastal flooding on a continuous global scale. We find that regions with limited water-level variability, i.e., short-tailed flood-level distributions, located mainly in the Tropics, will experience the largest increases in flooding frequency. The 10 to 20 cm of sea-level rise expected no later than 2050 will more than double the frequency of extreme water-level events in the Tropics, impairing the developing economies of equatorial coastal cities and the habitability of low-lying Pacific island nations.

Vulnerability Assessment of Hawai'i's Cultural Assets Attributable to Erosion Using Shoreline Trend Analysis Techniques

Abstract KANE, H.H.; FLETCHER, C.H.; ROMINE, B.M.; ANDERSON, T.R.; FRAZER, N.L., and BARBEE, M.M., 2012. Vulnerability assessment of Hawai′i′s cultural assets attributable to erosion using shoreline trend analysis techniques. Hawai‘i’s beaches are a focal point of modern lifestyle as well as cultural tradition. Yet coastal erosion threatens areas that have served as burial grounds, home sites, and other forms of cultural significance. To improve understanding of the convergence of erosion patterns and cultural uses, we mapped shoreline changes from Kawela Bay to Kahuku Point on the capital island of O‘ahu. Shoreline change rates are calculated from historical photographs using the single-transect (ST) and eigenbeaches (EX) method to define the 50- and 100-year erosion hazard zones. To ensure that shoreline change rates reflect long-term trends, we include uncertainties attributable to natural shoreline fluctuations and mapping errors. A hazard zone overlay was compared to cultural data provided by the Hawaii State Historic Preservation Division (SHPD) and the Office of Hawaiian Affairs (OHA) to identify threats to cultural features. Cultural features identified in the study include iwi kupuna (burials), Hawaiian artifacts, and Punaulua (a freshwater spring). Our analysis indicates that, except for Punaulua, all cultural features identified are vulnerable to coastal erosion at historical rates. The data produced in this study may be used as a proactive management tool to rank the vulnerability to threatened cultural features, as well as to develop protocols to appropriately manage cultural assets.

Q from pulse width of dispersed arrivals

Measurements of pulse width and travel time are used to estimate for dispersed arrivals. The method is based on propagating a reference wavelet with the constant-Q plane wave response using the phase velocity and travel path from the data. Differences in pulse width and travel time between the reference wavelet and the propagated pulse are used to construct a reference curve, called a Q-gram. The Q-gram, together with the measured pulse width increase in the data, gives the Q of the data.

Inversion for S-wave velocity from ODP sonic logging data

SUMMARY A recently published waveform inversion method is used to extract S-wave velocity from a few waveforms recorded in soft formations. A novel feature of the method is that it does not require estimates of the source and receiver transfer functions. This feature is useful for borehole problems as the sourcereceiver transfer functions may be different for different source-receiver pairs, and vary with depth due to changes of coupling with depth in the hole. actural values. Although Cheng’s spectral ratio eliminates the effects of the unknown source spectrum, it requires accurate estimates of the two receiver transfer functions. Recently Frazer & Sun (1998) presented waveform inversion techniques that are blind to the source wavelet and receiver transfer function. Their fourwise technique is developed here with reference to the LSS data. The LSS tool has two sources and two receivers (Fig 1), so at each depth only four full waveforms are recorded. THEORY

Migration of Seismic Data

Migration is one of those subjects that is difficult to explain to nonbelievers. The goal of migration is to generate an image of the subsurface velocity structure, but in order to migrate, one must first assume a velocity structure. Furthermore, until recently, nobody knew the meaning of the numbers output from migration; they were just numbers that made an image that looked more or less like the input data. The situation is further confused by the many different methods of migration: finite difference, Kirchhoff, F-K, phase shift, reverse time, dip move out (DMO), and others. It is possible to be an expert at one method of migration and understand almost nothing about the other methods. Migration is thus a kind of first aid: what to do while you wait for the mathematicians to arrive. Even the history of the subject is confused, mostly by the tendency of some petroleum companies to permit publication of research in only two instances: (a) when the are sure it will never work on data or (b) when they think the competition either already knows about it or is about to find out.