Yuh-Ing Chen

Variations of ionospheric total electron content during the Chi‐Chi Earthquake

On 20 September1999 UT (21 Septemberin local time, LT) a large earthquake Mw=7.7 struck central Taiwan nearthe small town of Chi-Chi. The greatest plasma frequency in the ionosphere, foF2, observed by the Chung- Li ionosonde (25.0 ◦ N, 121.2 ◦ E) reveals three clear precur- sors at 1, 3, and 4 days prior to the earthquake. This paper examines the ionospheric total electron content (TEC) ob- served by a network of the global positioning system (GPS) receivers in Taiwan area. It is found that variations in foF2 and overhead TEC recorded at Chung-Li have a similar ten- dency. Combining the data of the network of 13 GPS re- ceivers, time, and spatial variations of TEC prior to the Chi- Chi earthquake are examined. Results show that the equa- torial anomaly crest moves equatorward and its TEC value significantly decreases 1, 3, and 4 days before the earth- quake. A comparison between the disturbed and reference (previous 15-day median) days confirms that TEC decreases significantly around the epicenter in the afternoons of these days. Finally, possible mechanisms are proposed and dis- cussed.

Seismo‐ionospheric signatures prior to M≥6.0 Taiwan earthquakes

This paper examines variations of the greatest plasma frequency in the ionosphere, foF2, recorded by the Chung-Li ionosonde (25.0° N, 121.1° E) before M≥6.0 earthquakes during 1994–1999. The 15-day running median and the associated inter-quartile range are utilized as the reference and the upper or lower bounds to monitor the ionospheric foF2 variations for finding seismo-ionospheric signatures (precursors) of the earthquakes. It is found that precursors, in the form of the recorded foF2 falling below its associated lower bound around 1200–1700 LT, appear 1–6 days prior to these earthquakes. On September 20, 1999 UT (September 21, Taiwan local time) a large Mw=7.7 earthquake struck central Taiwan near the small town of Chi-Chi. We analyzed the foF2 and found three clear precursors 1, 3, and 4 days prior to the Chi-Chi earthquake.

A study on the background and clustering seismicity in the Taiwan region by using point process models

[1] This paper investigates the shallow seismicity occurring in the Taiwan region during the 20th century using a stochastic declustering method that has been developed on the basis of the theory of the epidemic-type aftershock sequence model. It provides a probability based tool to objectively separate the space-time occurrences of earthquakes into a background and a clustering component. On the basis of the background and clustering seismicity rates, we discuss the correlation between the distribution of the cluster ratio and the regional seismotectonic structures. Specifically, we find that the areas of the highest clustering ratio correspond to the major strike-slip fault traces in and around Taiwan. Additionally, in the Taiwan inland region, during the period 1960-1990, the outputs for the stochastically declustered catalogue show a clear quiescence in background seismicity preceding the recovery of activation and the occurrences of the 1999 Chi-Chi earthquake of M L 7.3, while the other active regions show stationary background activity. This could be interpreted as an effect of the aseismic slip in the Chi-Chi rupture fault, whereby the inland region around the Chi-Chi source becomes a stress shadow.

Atmospheric anomalies observed during earthquake occurrences

[1] Appearance of anomalies in the atmosphere before earthquakes (EQs) has been verified, through observation of anomalous transmission of VHF electromagnetic (EM) waves beyond line-of-sight. Anomalous increase of the received intensity for a few minutes - several hours on a day was identified by the previous 15-day running median and its inter-quartile range. The cross-correlation between the EQ occurrences and the anomalies shows that the appearance of anomalies was significantly enhanced within 5 days before M � 4.8 EQs. The one-day average number of the anomaly appearance within 5 days was found 2.4 times larger than that of other days. Through the polarization measurement of the received EM waves, the anomalies were found to occur in the atmosphere. INDEX TERMS: 6904 Radio Science: Atmospheric propagation; 6964 Radio Science: Radio wave propagation; 7223 Seismology: Seismic hazard assessment and prediction.Citation: Fujiwara, H., M. Kamogawa, M. Ikeda, J. Y. Liu, H. Sakata, Y. I. Chen, H. Ofuruton, S. Muramatsu, Y. J. Chuo, and Y. H. Ohtsuki (2004), Atmospheric anomalies observed during earthquake occurrences, Geophys. Res. Lett., 31, L17110,

The ionospheric perturbations prior to the Chi-Chi and Chia-Yi earthquakes

Abstract In this paper we analyze the greatest plasma frequency, foF2, named critical frequency, observed by the Chung-Li ionosonde (25.0°N, 121.l°E) during the period of the Chi-Chi (23.87°N, 1 20.75°E) and the Chia-Yi (23.51°E, 120.4°E) earthquakes. The previous 15-day running mean and the associated standard deviation are utilized to construct the upper or lower bound for detecting the seismo-ionospheric perturbations. It is found that the perturbation appeals in 3–4 days prior to the Chi-Chi earthquake as well as 1–3 days prior to the Chia-Yi earthquake.

Ionospheric foF2 variations prior to strong earthquakes in Taiwan area

Abstract Many studies of the seismo-ionospheric coupling effects have been reported. On 17 July 1998(M=6.2), 20 September 1999 (M=7.3) and 22 October 1999 (M=6.4) three large earthquakes respectively struck Rei-Li, Chi-Chi and Chia-Yi in central Taiwan. The three earthquakes severely damaged structures, heavily changed landforms and disturbed geophysical environments. This paper examines variations of the ionospheric penetration frequency, foF2 , observed by Chung-Li ionosonde station (25.0° N, 121.1° E) several days before the three earthquakes. The mean- and median-based statistical techniques are introduced to investigate the ionospheric electron density prior to the three earthquakes. Results show that the foF2 decrease significantly before the three earthquakes.

Nonparametric procedures for comparing umbrella pattern treatment effects with a control in a one-way layout.

In this paper we are concerned with comparing umbrella pattern treatment effects with a control in a one-way layout. The problem of testing whether there is at least one treatment that is better than the control is considered. Distribution-free tests are proposed for both cases where the peak of the umbrella is known or unknown. Approximate small-sample critical values are presented and the results of a Monte Carlo power study are discussed.

Nonparametric comparisons of umbrella pattern treatment effects with a control in a one-way layout

Nonparametric tests for comparing umbrella pattern treatment effects with a control in a one-way layout were studied in Chen and Wolfe (1993). In this paper a recursive formula for deriving the isotonic regression which is useful for statistical inference under the umbrella pattern restriction is given. An alternative multiple test procedure is then considered for the setting where the peak of the umbrella is known. The results of a Monte Carlo power study are presented

Modifications of the Mack-Wolfe umbrella tests for a generalized Behrens-Fisher problem

We are concerned with testing procedures for umbrella alternatives in the k-sample location problem without making the assumption that the underlying populations have the same shape. Modifications of the Mack-Wolfe tests are proposed for the cases when the peak of the umbrella is known or unknown. The proposed procedures are exactly distribution-free when the continuous populations have the same shape. The modified test for peak-known umbrella alternatives remains asymptotically distribution-free when the continuous populations are symmetric, but not necessarily with the same shape.

Multiple comparisons in carcinogenesis study with right-censored survival data.

This paper considers the practical problem in animal carcinogenesis experiments where several treatment groups are compared with a control group in a one-way layout and the observed survival data are subject to random right-censorship. Proposed herein are multiple testing procedures based on two-sample weighted logrank statistics, each comparing an individual treatment with the control, for determining which treatments are more effective than the control. The associated p-value of claiming a certain treatment is more effective than the control is also discussed. A test-based confidence set for the scale changes between each treatment and the control is then obtained. The comparative results of a Monte Carlo error rate and power study for small sample sizes are presented. Finally, a numerical example involving renal carcinoma in mice demonstrates the feasibility of the proposed multiple testing procedures and test-based confidence set.